I became an atheist by growing into it. When I was 9 a school friend introduced me to science fiction via Robert Heinlein's "Have Space Suit, Will Travel". I'd always liked to read, but this opened up an entire new universe to me. By the end of the school year I'd read ever science fiction book in the school library and had been introduced to Isaac Asimov and Arthur C. Clarke along the way. This led to Asimov's science books and an avid interest in astronomy. Over the next few years I started seeing obvious problems with reality, the Natural Universe, and what was being taught to me every Sunday morning in Bible school. By the time I was a HS Sophomore (and a typical teenager) I was a fervent atheist.
I wasn't an asshole about it. I simply didn't believe. What others believed was their problem. However, when asked, I wasn't shy about my beliefs. This led to a small intervention with my parents and two elders from my church. Everyone was nice about it. They just wanted to talk and talk we did. It was very congenial, but definitely in the category of "agreeing to disagree" since no opinions were changed after the discussion.
The following year I had a near death experience. No tunnel of light or magical beings, but definitely a most memorable experience. Very real. I'd been knocked out, had vivid dreams and other (much later, ahem, altered states) experiences of consciousness, but nothing matched that before or since.
It didn't make me believe in God and nor do I conform to what passes for American Christianity (especially Baptists!), but it did put me on a spiritual journey that will have lasted 40 years this winter.
I don't believe in magical sky daddies but I also don't believe people like Richard Dawkins are as smart as they think they are. I believe mankind, if not everything else in the Universe has a spiritual component. How and why I have no idea, but I do think it all fits together somehow.