I had a flashback to a fundie troll I once dueled with named Annie. She was a crazy mom who repeatedly argued that the atheist readers of the blog chose to become atheists because we wanted to lead a sinful life. That's what she told her children, and we called her a liar for it. I wish I thought to phrase my rebuttals the way I'm going to write this post:
Fundamentalists live in a culture of permissiveness that disgusts us. That disgust is what motivated me to stop attending church. There were a number of moral boundaries I refused to cross, and I refused to associate with anyone who took such a flippant, frivolous attitude towards those boundaries.
The doctrine of Hell requires a permissive attitude towards torture.
Annie's atheist concentration camps (I believe she actually used the phrase "concentration camps"!) require a permissive attitude towards killing and religious persecution.
Creationism requires a permissive attitude towards deception.
Belief that god ordered the wars described in the Old Testament requires a permissive attitude towards genocide.
Belief that god's will is our purpose for living requires a permissive attitude towards slavery.
Belief that our humanity is defined at the moment of conception, in my experience with pro-lifers, appears to require a permissive attitude towards eugenics: The ones I've dealt with essentially were arguing that our DNA defines whether or not we're a person, not our thoughts, emotions, and consciousness.
Belief in the fables about people "cursed" or "chosen" by god was used to establish and maintain a culture of permissiveness towards slavery, murder, and racism.
Belief in the dominance of one sex over another was, and is currently being used to maintain a culture of permissiveness towards rape.
Belief in the value of faith requires a permissive attitude towards hubris and the idea that a person can be infallible and beyond question. In other words, faith is the act of believing oneself to be the supreme being. All the other vices owe a lot towards this attitude.