Religion *is* a cultural constraint
It's one of the biggies, but not the source. I look at it this way:
There comes a time in the development of every culture when the population gets so big that "Because I said so" no longer works for the leaders. So they transform what had been a collection of 'nature spirits', if you will, into a Boss. Then it becomes "Because the god(s) said so".
The rules themselves developed before the religions were invented to intensify their enforcement. After all, we've been social since before we were human, and we've always needed rules for getting along. Just our luck, not to have records older than scripture... so we assume the religions made the rules, not the other way around.