A lot of you probably share my primary reason: coming out is just too much trouble.
I became an atheist shortly before I left for college, but I had a lot of friends at church, and my parents are serious Christians. I thought I could wait until I got to college to tell them. I had no problem with being open to new friends at school, but I kept putting off telling people in my home town about my deconversion. Now I'm back for the summer after an academic year, and the situation hasn't changed - they all think I'm a committed Christian.
Unfortunately, I never made many close friends in high school, so the only people I'm still regularly in contact with are friends from church. I want to be able to express my honest opinion, but I value their friendship more than my own integrity at the moment - I am not an introvert, so a summer alone would be worse for me than a summer of pretending to believe a lie.
This thread isn't just for me. Share away.