[jmgurgeh]

First of all, threat of retribution is not a sufficient, necessary, or even a very effective means of controlling people, as has been shown time after time. People act good out of preference for acting good, or vice versa. Why do I abstain from doing evil things? Because I don't want to be evil.

I think the problem is when somebody falls into the middle ground. They aren't sure if something is really bad or they don't have a very strong conviction, and they end up rationalizing it to themselves. Not that you implied this in your post (just as an aside), to think that atheists fall into that category more than theists is insanity.