I never exactly thought of belief being a choice. It really isn't. We choose to be Atheists/Agnostics/Others because we have reason to believe such just like Christians and others have a reason to believe. Now whether that's experience or knowledge, or location, that just plays as a factor.
However, if you go up to me and ask why I don't believe in God, I'd tell you that I don't have any reason to nor supporting evidence of it.
I bet if you ask a religious person though, they'd tell you things like how they were raised to be such or they like having faith or it just makes sense to them.
So when we get down to it, all our beliefs are tied down to these little bits of information and personal wants that lead down to "This is what makes most sense to me."
We may be able to say that THAT idea is stupid or we don't believe, but we still don't play a factor in what makes sense to a person. Just us.