The Immaculate Conception of Mary was infallibly defined by Pope Pius IX (1792-1878 AD) as a dogma in his Encyclical Ineffabilis Deus:
Pope Pius IX - Ineffabilis Deus (1854 AD)
Wherefore, in humility and fasting, we unceasingly offered our private prayers as well as the public prayers of the Church to God the Father through his Son, that he would deign to direct and strengthen our mind by the power of the Holy Spirit. In like manner did we implore the help of the entire heavenly host as we ardently invoked the Paraclete. Accordingly, by the inspiration of the Holy Spirit, for the honor of the Holy and undivided Trinity, for the glory and adornment of the Virgin Mother of God, for the exaltation of the Catholic Faith, and for the furtherance of the Catholic religion, by the authority of Jesus Christ our Lord, of the Blessed Apostles Peter and Paul, and by our own: "We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instance of her conception, by a singular grace and privilege granted by Almighty God, in view of the merits of Jesus Christ, the Savior of the human race, was preserved free from all stain of original sin, is a doctrine revealed by God and therefore to be believed firmly and constantly by all the faithful."
Hence, if anyone shall dare - which God forbid! - to think otherwise than as has been defined by us, let him know and understand that he is condemned by his own judgment; that he has suffered shipwreck in the faith; that he has separated from the unity of the Church; and that, furthermore, by his own action he incurs the penalties established by law if he should dare to express in words or writing or by any other outward means the errors he thinks in his heart.
Above is universally recognized to be Ex Cathedra - the Pope employing the power, as would be defined by Vatican 1 (1870 AD), to infallibly define dogma, which must be believed by all the faithful on pain of Anathema. It teaches that if anyone does not believe that Mary was conceived without Original Sin, then they are "separated from the unity of the Church" - "outside of which there is absolutely no Salvation" (Fourth Lateran Council, 1215 AD).
There are many verses in the Bible stating that all have sinned (Romans 3:10-12, 3:23, 5:12, Psalm 14:2-3, Galatians 3:22, Ecclesiastes 7:20: 1 Kings 8:46). As far as exceptions are concerned, as is discussed in this article, infants, and the mentally ill, are in a state of innocence regarding the sins that they may commit, and therefore, those sins are not imputed to them.
There is no Biblical evidence, however, that Mary was somehow exempt from having had a sinful nature inherited from Adam, or even for the idea that she never committed actual sins. Rather, Mary was still alive Christ said "there is none good but one, that is, God" (Matthew 19:16-17, Mark 10:17-18, Luke 18:18-19). Could Christ have said this, if Mary was in fact utterly sinless, never even having been born with a sinful nature? How would such a person not be "good", in the absolute sense, which Christ here specifically says only applies to God?
Further, Mary acknowledged that she needed a Savior in Luke 1:46-47. And, the angel had instructed her to name her baby "Jesus: for He shall save His people from their sins" (Matthew 1:21). There is no indication, anywhere in Scripture, that Mary was referring to some non-ordinary concept of Salvation from her personal sins, when she confessed that she had a "Savior".
Finally, in Luke 2:22-24, Mary goes to the Temple "to offer a sacrifice according to that which is said in the law of the Lord, A pair of turtledoves, or two young pigeons" (Luke 2:24). Then, in the Law, we read:
Leviticus 12:6-8
6 And when the days of her purifying are fulfilled, for a son, or for a daughter, she shall bring a lamb of the first year for a burnt offering, and a young pigeon, or a turtledove, for a sin offering, unto the door of the tabernacle of the congregation, unto the priest:
7 Who shall offer it before the LORD, and make an atonement for her; and she shall be cleansed from the issue of her blood. This is the law for her that hath born a male or a female.
8 And if she be not able to bring a lamb, then she shall bring two turtles, or two young pigeons; the one for the burnt offering, and the other for a sin offering: and the priest shall make an atonement for her, and she shall be clean.
Mary made a sin offering, because she was a sinner. This would have been a fantastic opportunity, if she were sinless, for the Lord to have pointed that out, in some way - either by a modified offering, or an explanation as to why she didn't really need to offer the sin offering. But, that is totally absent.
As for addressing Roman Catholic prooftexts for this doctrine, see Chapter 13's discussion of Luke 1:28, 1:42, and Genesis 3:15 in my review of The Roman Catholic Controversy, by James White.
To summarize, there is no Biblical support whatsoever for Mary being sinless, let alone for her having been conceived without a sinful nature. And, there are many positive indications that she was a sinner, who needed a Savior, just as everyone else.
There are two categories of quotations from Church history that disprove the doctrine of the Immaculate Conception:
Because there are so many quotations for the first category, they will be relegated to Appendix I. This section will focus on the statements in which sins, or a sinful nature, are explicitly ascribed to Mary.
Origen (185-253 AD), in his commentary on Luke 2:35, says the following:
Origen (185-253 AD) - Homilies on Luke 17:6-7
6 Thereupon Simeon says, "a sword will pierce your very soul". Which sword is this that pierce not only others' hearts, but even Mary's? Scripture clearly records that, at the time of the Passion, all the apostles were scandalized. The Lord himself said, "This night you will all be scandalized". Thus, they were all so scandalized that Peter too, the leader of the apostles, denied him three times. Why do we think that the mother of the Lord was immune from scandal when the apostles were scandalized? If she did not suffer scandal at the Lord's Passion, then Jesus did not die for her sins. But, if "all have sinned and lack God's glory, but are justified by his grace and redeemed, then Mary too was scandalized at that time.
7 And this is what Simeon now prophesies when he says, "And your very soul". You know, Mary, that you bore as a virgin, without a man. You heard from Gabriel, "The Holy Spirit will come upon you, and the power of the Most High will overshadow you." The "sword" of infidelity "will pierce" you, and you will be struck by the blade of uncertainty, and you thoughts will tear you in pieces when you see him.
John Chrysostom (347-407 AD), a Saint and Doctor of the Church, in his commentary on Matthew 12:46-49, says the following:
John Chrysostom (347-407 AD) - Homily 44 on Matthew
And this is hence especially manifest. "For while He yet talked to the people", it is said, "one told Him, Your mother and Your brethren seek You". But He says, "who is my mother, and who are my brethren?"
And this He said, not as being ashamed of His mother, nor denying her that bare Him; for if He had been ashamed of her, He would not have passed through that womb; but as declaring that she has no advantage from this, unless she do all that is required to be done. For in fact that which she had essayed to do, was of superfluous vanity; in that she wanted to show the people that she has power and authority over her Son, imagining not as yet anything great concerning Him; whence also her unseasonable approach. See at all events both her self-confidence and theirs. Since when they ought to have gone in, and listened with the multitude; or if they were not so minded, to have waited for His bringing His discourse to an end, and then to have come near; they call Him out, and do this before all, evincing a superfluous vanity, and wishing to make it appear, that with much authority they enjoin Him. And this too the evangelist shows that he is blaming, for with this very allusion did he thus express himself, While He yet talked to the people; as if he should say, What? Was there no other opportunity? Why, was it not possible to speak with Him in private?
Augustine (354-430 AD), a Saint and Doctor of the Church, wrote:
Augustine (354-430 AD) - De Genesi Ad Litteram, Book 10, Chapter 18
Accordingly, the body of Christ was truly assumed from the women's flesh, which is from her flesh of sin propagated from her conception. Nevertheless, because His body does not follow her conception in this same way, He is not her flesh of sin, but the likeness of the flesh of sin. It is asserted the Body of Jesus has not received death from thence, which appears to be not aroused from the flesh's will, as much His will overcame his spirit yearning against that flesh, because His body does not have the contagion of sin. But which this body discharges death as a debt not owed, and it exhibits the foundation for the promised resurrection - which one we do not fear the other resurrection the worthy hope for.
Fulgentius of Ruspe (460-533 AD), who is a Saint, wrote the following:
Fulgentius of Ruspe (460-533 AD) - Epistle 17, Chapter 6
This is the grace whereby it came to pass that God, Who came to take away sins, because sin was not in Him, was conceived and born a man in the similitude of sinful flesh. The flesh of Mary, forsooth, which had been conceived in iniquities after the manner of men, was indeed sinful flesh, which bore the Son of God in the similitude of sinful flesh. We must believe that the Only begotten God did not derive the defilement of sin from the mortal flesh of the virgin. Truly, therefore, Mary conceived God the Word, which she bore in sinful flesh, which God received.
Bernard of Clairvaux (1090-1153 AD), a Saint and Doctor of the Church, lived during a time in which the doctrine was already being advocated for, and he writes:
Bernard of Clairvaux (1090-1153 AD) - Letter 45, To the Canons of Lyons, on the Conception of Saint Mary
6 And if it is permitted to say what the Church thinks, and the Church thinks that which is true, I say that she conceived by the Holy Spirit, but not that she was conceived by Him; that she was at once Mother and Virgin, but not that she was born of a virgin. Otherwise, where will be the prerogative of the Mother of the Lord, to have united in her person the glory of maternity and that of virginity, if you give the same glory to her mother also? This is not to honour the Virgin, but to detract from her honour. If, therefore, before her conception she could not possibly be sanctified, since she did not exist, nor in the conception itself, because of the sin which inhered in it, it remains to be believed that she received sanctification when existing in the womb after conception, which, by excluding sin, made her birth holy, but not her conception.
7 Wherefore, although it has been given to some, though few, of the sons of men to be born with the gift of sanctity, yet to none has it been given to be conceived with it. So that to One alone should be reserved this privilege, to Him who should make all holy, and coming into the world, He alone, without sin should make an atonement for sinners. The Lord Jesus, then, alone was conceived by the Holy Ghost, because He alone was holy before He was conceived. He being excepted, all the children of Adam are in the same case as he who confessed of himself with great humility and truth, I was shapen in iniquity, and in sin hath my mother conceived me (Psalm 51:5).
8 And as this is so, what ground can there be for a Festival of the Conception of the Virgin? On what principle, I say, is either a conception asserted to be holy which is not by the Holy Ghost, not to say that it is by sin, or a festival be established which is in no wise holy? Willingly the glorious Virgin will be without this honour, by which either a sin seems to be honoured or a sanctity supposed which is not a fact. And, besides, she will by no means be pleased by a presumptuous novelty against the custom of the Church, a novelty which is the mother of rashness, the sister of superstition, the daughter of levity.
Thomas Aquinas (1224-1274 AD), a Saint and Doctor of the Church, likewise lived while this doctrine was being advocated for, and in his most important work, the Summa Theologica, he explicitly rejects it:
Thomas Aquinas (1224-1274 AD) - Summa Theologica, Part 3, Question 27, Article 2
The sanctification of the Blessed Virgin cannot be understood as having taken place before animation, for two reasons. First, because the sanctification of which we are speaking, is nothing but the cleansing from original sin: for sanctification is a "perfect cleansing," as Dionysius says (Div. Nom. xii). Now sin cannot be taken away except by grace, the subject of which is the rational creature alone. Therefore before the infusion of the rational soul, the Blessed Virgin was not sanctified.
Secondly, because, since the rational creature alone can be the subject of sin; before the infusion of the rational soul, the offspring conceived is not liable to sin. And thus, in whatever manner the Blessed Virgin would have been sanctified before animation, she could never have incurred the stain of original sin: and thus she would not have needed redemption and salvation which is by Christ, of whom it is written (Matthew 1:21): "He shall save His people from their sins." But this is unfitting, through implying that Christ is not the "Saviour of all men," as He is called (1 Timothy 4:10). It remains, therefore, that the Blessed Virgin was sanctified after animation.
Thomas Aquinas (1224-1274 AD) - Summa Theologica, Part 3, Question 27, Article 2
If the soul of the Blessed Virgin had never incurred the stain of original sin, this would be derogatory to the dignity of Christ, by reason of His being the universal Saviour of all.
Thomas Aquinas (1224-1274 AD) - Summa Theologica, Part 3, Question 27, Article 2
Sanctification is twofold. One is that of the whole nature: inasmuch as the whole human nature is freed from all corruption of sin and punishment. This will take place at the resurrection. The other is personal sanctification. This is not transmitted to the children begotten of the flesh: because it does not regard the flesh but the mind. Consequently, though the parents of the Blessed Virgin were cleansed from original sin, nevertheless she contracted original sin, since she was conceived by way of fleshly concupiscence and the intercourse of man and woman: for Augustine says (De Nup. et Concup. i): "All flesh born of carnal intercourse is sinful."
Notice also in the last quotation above, he cites Augustine's De Nuptiis Et Concupiscentia (On Marriage and Concupiscence).
In summary, the early witness of Origen, in addition to the teaching of five Saints, four of which are Doctors of the Catholic Church, is explicitly contrary to the dogma promulgated by Pope Pius IX in 1854 AD.
The dogma of the Immaculate Conception, much like the Assumption of Mary, is unbiblical, and ahistorical. Yet, the Catholic Church has bound it to the conscience of every professing Christian, on pain of anathema. This is a demonstration of the type of abuse that can take place when Sola Scriptura is abandoned in favor of Sola Ecclesia.
Clement of Alexandria (150-215 AD) - The Instructor, Book 1, Chapter 2
2 He is wholly free from human passions; wherefore also He alone is judge, because He alone is sinless. As far, however, as we can, let us try to sin as little as possible.
Clement of Alexandria (150-215 AD) - The Instructor, Book 3, Chapter 12
12 Further, He banishes utterly love of glory, saying, "Woe to you, Pharisees! for ye love the chief seat in the synagogues, and greetings in the markets." But He welcomes the repentance of the sinner - loving repentance - which follows sins. For this Word of whom we speak alone is sinless. For to sin is natural and common to all. But to return [to God] after sinning is characteristic not of any man, but only of a man of worth.
Tertullian (160-220 AD) - A Treatise on the Soul, Chapter 41
41 Thus some men are very bad, and some very good; but yet the souls of all form but one genus: even in the worst there is something good, and in the best there is something bad. For God alone is without sin; and the only man without sin is Christ, since Christ is also God. Thus the divinity of the soul bursts forth in prophetic forecasts in consequence of its primeval good; and being conscious of its origin, it bears testimony to God (its author) in exclamations such as: Good God! God knows! and Good-bye! Just as no soul is without sin, so neither is any soul without seeds of good.
Tertullian (160-220 AD) - Prescription against Heretics, Chapter 3
3 For to the Son of God alone was it reserved to persevere to the last without sin.
Cyril of Jerusalem (315-386 AD) - Catechetical Lecture 2
10 For we tell some part of what is written concerning His loving-kindness to men, but how much He forgave the Angels we know not: for them also He forgives, since One alone is without sin, even Jesus who purges our sins. And of them we have said enough.
Ambrose (339-397 AD), cited by Augustine (354-430 AD) - On the Grace of Christ, and on Original Sin, Book 2, Chapter 47
47 The same holy man also, in his Exposition of Isaiah, speaking of Christ, says: "Therefore as man He was tried in all things, and in the likeness of men He endured all things; but as born of the Spirit, He was free from sin. For every man is a liar, and no one but God alone is without sin. It is therefore an observed and settled fact, that no man born of a man and a woman, that is, by means of their bodily union, is seen to be free from sin. Whosoever, indeed, is free from sin, is free also from a conception and birth of this kind". Moreover, when expounding the Gospel according to Luke, he says: "It was no cohabitation with a husband which opened the secrets of the Virgin's womb; rather was it the Holy Ghost which infused immaculate seed into her unviolated womb. For the Lord Jesus alone of those who are born of woman is holy, inasmuch as He experienced not the contact of earthly corruption, by reason of the novelty of His immaculate birth; nay, He repelled it by His heavenly majesty."
Augustine (354-430 AD) - On Merit and the Forgiveness of Sins, and the Baptism of Infants, Book 2, Chapter 47
47 This being the case, ever since the time when by one man sin thus entered into this world and death by sin, and so it passed through to all men, up to the end of this carnal generation and perishing world, the children of which beget and are begotten, there never has existed, nor ever will exist, a human being of whom, placed in this life of ours, it could be said that he had no sin at all, with the exception of the one Mediator, who reconciles us to our Maker through the forgiveness of sins.
Pope Leo I (400-461 AD) - Sermon 25, The Nativity of the Lord
5 Therefore the catholic faith acknowledges the Lord's glory in his humility, and the Church, which is the body of Christ, rejoices in the sacraments of its salvation; for if the Word of God had not become flesh and dwelt among us, if the Creator had not descended to communion with the creature, and recalled the old man to a beginning in his birth, death would have reigned from Adam (Cf. Rom 5:14) until the end, and condemnation would have remained indestructibly on all man, when by the condition of birth, there is one cause of perishing for all. And so among the sons of men, the Lord Jesus alone was born innocent, since he alone was conceived without the pollution of carnal concupiscence. He became a man of our race, so that we might be able to be partakers of the divine nature. He took an origin in the womb of the Virgin, was placed in the baptismal font; he gave to the water, what he gave to his mother; for the power of the Most High and the overshadowing of the Holy Spirit, which worked that Mary gave birth to the Savior, also worked that water regenerate the believer.
Pope Gregory I (540-604 AD) - An Exposition on the Book of Blessed Job, Book 18
84 For we, though we are made holy, yet are: not born holy, because by the mere constitution of a corruptible nature we are tied and bound, that we should say with the Prophet, Behold, I was shapen in wickedness, and in sin hath my mother conceived me. But He only is truly born holy, Who in order that He might get the better of that same constitution of a corruptible nature, was not conceived by the combining of carnal conjunction.
Roman Clergy circa 630 AD - Bede's Ecclesiastical History, Book 2, Chapter 19
For who would not detest that insolent and impious assertion, 'That man can live without sin of his own free will, and not through the grace of God?' And in the first place, it is blasphemous folly to say that man is without sin, which none can be, but only the one Mediator between God and men, the Man Christ Jesus, Who was conceived and born without sin; for all other men, being born in original sin, are known to bear the mark of Adam's transgression, even whilst they are without actual sin, according to the saying of the prophet, 'For behold, I was conceived in iniquity; and in sin did my mother give birth to me.'