I cannot believe in a deity of any kind. I can no more choose belief than I can choose to sneeze. Belief or nonbelief is an involuntary action. You can certainly fake either-or - but you always know.

I never made a conscious decision to be an atheist when I was growing up. I just realised that I didn't believe that there was a God. It wasn't via lack of exposure - when I was young, and incapable of holding a religious opinion (I hadn't matured enough that I could think about such things), I used to go to church regularly - my mother is Catholic. I just didn't believe. I have some suspicions about why this is so - early exposure to science and critical thinking is my best guess - but that's mostly irrelevant to the point I'm trying to make here, which is that I am literally incapable of belief in God, in just the same way that I cannot fly unaided.

Why is this important?

Consider how much religious apologetics depends on belief being a choice. The 'free will' argument commonly asserted as the reason for the existence of evil in a world with a benevolent God and the reason he doesn't make his presence more obvious, for starters. If I cannot choose belief, God's presence doesn't reduce my free will in the slightest - although it certainly means that I'd be a believer.

Consider, also, what it does to the concept of Hell - already a pretty brutal concept that's damned hard to explain in a way that makes God a moral character (The best one I've heard is that Hell is simply the absence of God, and that I'm not going to want him around because I don't believe in him. This rather sidesteps the obvious point that it's not that I don't hate God, I just don't think he exists, although he'd have to give some pretty good answers to a few questions before I'd be happy). Now, Hell is no longer even a punishment for making a bad decision - it's a punishment for a property you had no control over. If Hell was the mandated punishment for all people with blue eyes, or all myopic people, it'd be pretty obvious that it was stupid. If belief is just as much not your choice, why is it any different?

Does this make argument and debate useless? Well, no. I'm not saying your beliefs can change - I'm simply saying that you can't consciously decide to change them.