I grew up Catholic, and had argued myself to the “correct” conclusion, that the Church’s teachings and morality were soundly defensible via logic. During college, however, my views on morality, especially but not limited to sexual morality, changed, forcing me to re-evaluate the logical connections I had previously accepted. (I remember vividly one time, while riding a horse into Damascus, reading a speech of Douglas Adams where he forcefully argues that calling masturbation wrong on the grounds that it does harm is not only false but unconscionably cruel.) I became convinced that humans have the power and the right to decide on what is just and moral together — that no god worthy of the name would give moral edicts at all, and certainly not ones merely reinforcing old, old prejudices.
I am an atheist because I became convinced that god was a story we invented. But I call myself an atheist because I do believe in something: I believe that we can do better.