I'm an unapologetic atheist from a very Christian family raised in a very Christian environment. I was a Pentecostal Christian growing up, and rejected Christianity somewhat gradually between my last year of high school and first few years of college. I'm a software developer and very interested in cognitive sciences, and I believe the skills and mindsets entailed in both of those have contributed to my rejecting Christianity.
Why I Am Not a Christian/Theist
I was a very intrinsic Christian through high school. I never exactly "blindly accepted" my beliefs, but the answers I had at the time were enough to counter what doubts I did have. I did have one kind of fundamentalist belief: I unconsciously assumed that the Bible was "inspired" to such a degree that it was practically a dictation directly from God. Throughout high school, I realized how implausible that sounded, and I began asking questions and having doubts about the canon.
From there, I started having doubts from two other directions: first, I wondered why do so many people believe different things in different parts of the world, and second, I became convinced that most people's reasons for holding religious beliefs aren't very good.
The "problem of evil" was never a factor for me, unlike a lot of people around me. I think the fairytale notion of a painless world seems almost unintelligible, and it makes sense to me that the potential for good entails the potential for evil. If anything, I had trouble imagining a heaven where anything mattered, without the potential for failure or improvement. But maybe I'd feel differently if I had experienced more tragic loss.
Once I rejected Christianity, I saw nothing compelling in any other religions. I see no reason to seek out a god in hiding, and none of the major world religions looked any better than Christianity.
I do, however, find a certain charm in Zen Buddhism and its teachings, and I've experimented with meditation. I see no reason to reject self-discipline, mental focus, and occasional reverence along with belief in God.