My personal experience contends that, and most of the atheists I currently know. No, actually all of them were at one point religious. I don't know anyone that grew up in an atheist household, but I don't seem to have any trouble coming across people who have, upon their own investigations, rejected their religion and the notion of faith in favor of reason.

I know I don't speak on his behalf, but from what I remember from my brother, he could have been considered a fundamentalist Christian. Walk up to his desk now and you're likely to see a copy of "God is Not Great" by Christopher Hitchens or perhaps "The God Delusion" by Richard Dawkins. I have known others who came to same conclusions, and I doubt those authors explaining atheism had no part in ridding misconceptions behind atheism.

Michael Shermer, for example, well-known advocate for skepticism (Skeptic Magazine) and atheism, was once a Christian fundamentalist.

Actually, it's my contention that the ruthlessness of fundamentalism (an expression, not a perversion, of a particular faith) drives people with a conscience to question their faith, which leads them to the many philosophers of atheism and religious skepticism from the classics such as Empiricus, Democritus, Lucretius, to David Hume, Darwin, Mark Twain, to today's Albert Einstein, Carl Sagan, Richard Dawkins, and the like.