Oddly enough, politics was the catalyst for me.

I grew up in a very religious, very conservative Mormon family. From my father I acquired the attitude that there are few things more shameful than dishonesty. From reading science fiction, particularly Asimov and Heinlein, and reading science books, I acquired the ideal of intellectual honesty. My father had very strong religious and political opinions that brooked no dissent. In attempting to formulate a consistent political philosophy of my own, I found my opinions diverging from his, but I lacked the courage to openly contradict him. After I had been away from home for several years, in my early twenties, I went through a period where I made a serious effort to root out any inconsistencies in my political philosophy and just honestly follow the consequences of my principles wherever they led. I ended up a libertarian anarchist.

I didn't know it at the time, but that was the beginning of the end for my religious beliefs. Intellectual honesty had long been an ideal for me; now it was an important part of my self-image. I found that I could no longer ignore the special pleading I engaged in when it came to my religious beliefs. If I applied to my religious beliefs the same standards I used to evaluate non-religious claims, they started to look pretty shaky. But everyone in my family and everyone in my social circle was Mormon. I had spent a year and a half as a missionary for the Mormon church. My wife was a devout Mormon. I had just started my graduate studies at BYU, a university owned by the Mormon church.

And my father reserved his most vociferous condemnation for "apostates".

The critical point came when I was 28, during an interview with my bishop for a temple recommended. One of the questions he asked was, "Do you believe in God the Father, and in his son Jesus Christ, and in the Holy Ghost?" I realized that, in fact, I did not, and my upbringing did not allow me to lie about it. I went home without a temple recommend... and then had to explain to my wife why.

Everything else since then has just been filling in the details.