The article Why I'm Not an Atheist explains why I am not the type of Agnostic that is unsure if God even exists in the first place. This article deals with why I'm not the kind of Agnostic who doesn't adhere to any particular religion despite acknowledging the existence of God.
Since people exist, God is directly responsible for them existing. In this situation, they suffer extremely disproportionately, meaning some of them get off light even though they do bad things, whereas some of them suffer horribly and are innocent (kids) or have done comparatively little harm to one another.
God allows this situation, which I discuss in detail here, to exist, even though He could rectify it immediately, and make it perfectly just.
Since this is the case, if the Creator doesn't bring humanity into some type of judgement where their deeds and circumstances are accounted for, then God is content with things being unfair, egregiously, forever, with no consolation or justice.
In that circumstance, God created a being that wants to experience joy, fairness, and happiness, but He leaves them alone in pain, suffering, and injustice, even though He could stop it, and He'll never rectify any of it. If this is the case, then humans as a species are hopeless, because the God of this universe is a sadist.
Therefore, we are forced to operate on the assumption that there will be a judgement. And, this judgement must take place after death. Anyone who can look around and see the horrible suffering that so many people have to endure on this earth caused by corrupt leaders, murderers, and other people should be able to tell right away that not everyone - in fact, almost no one - gets what they deserve in terms of consequences here in this life. If there's a final, divine judgement, it definitely isn't down here during our lives.
Consider for a moment someone like Joseph Stalin. He is a man that destroyed millions upon millions of lives through murder, starvation, war, and imprisonment. Yet, he died in his home at the age of 74 after a relatively brief illness. He was never brought to justice, even though the situation demands it. That's because the judgement comes afterwards.
Every Agnostic that believes there is a God will deny this. They think that if there is a judgement, it's just going to be based on some abstract "were you a good person?" type of criteria, and that's all that we can operate on.
Immediately, questions arise:
If after we die, we are going to be judged, and we can't know any of the criteria or consequences ahead of time, then we are in a similar situation to if God doesn't judge us at all, in the sense that we are likewise doomed and hopeless. He could make up any criteria for the judgement on the spot. A surprise judgement, with secret criteria, and hidden consequences, is absurdly unfair.
A "God" that would make this planet, make us, and then leave us without bothering to communicate with us at all, has put us in a hopeless situation - doomed to wander on this violent, painful, wicked earth without any instructions, never having peace, never knowing if we are pleasing Him or making Him madder, or even what does which in the first place.
I am not an Agnostic because I believe that God will be just with his creation, and that requires a judgement. Similarly, I believe that a judgement requires a warning so that we can know what will be involved once we get to it. I don't believe that God made us and then left us here without communication or revelation.
Every Agnostic should also be aware that, by refusing to choose a religion, they have not remained "neutral" at all. They are in a religion that is actively anti-Christian, according to Jesus Christ Himself:
Matthew 12:30
30 He that is not with me is against me; and he that gathereth not with me scattereth abroad.
There is no option of remaining neutral, as God sees it. By not believing in Jesus, you have, either implicitly or explicitly, rejected hundreds of the claims of God and Jesus Christ, and are therefore anti-Christian.
Atheists and Agnostics both, then, have not traded in religion for no religion. They make the religious claim that Jesus was a false prophet, by refusing to believe in Him, according to Himself. If they reject they are doing so, they make the religious claim that Christ's assertion about this was a lie. Atheism and Agnosticism are therefore anti-Christian religions, their false claims to apathy notwithstanding.