St. Anselm made a very intricate argument for the impossibility of true disbelief in God in his Prosologion.
Here's the link to the wikipedia entry on him. Essentially, he argued that the reality of God was inherent in the concept of 'God', because God is greater then everything, and a real God is greater then a made-up God. Only it's longer and much more beautiful then that.
This argument seems very convincing to me, but I had mystical encounters with God, and sought reasons to believe in God afterwards.
Of course this doesn't mean that you can't choose not to believe in God, but from by viewpoint this disbelief is profoundly illogical.
Furthermore, from my viewpoint, some atheists do seem to be more angry at the Church then convinced that God does not exist- they'll bring up the violence of the Crusades as a reason why religion is bad, seemingly oblivious to the fact that if Christianity is true, then flaws in the Church become entirely irrelevant.