But I don't think you need to be religious to be moral.
You are missing that the "choose freely" depends entirely upon fear of ostracism, upon societal coercion. Upon a relatively closed society where disgrace and gossip can ruin lives. Upon "what the neighbors will say". Lets take an example. Libertarians go on and on about the superiority of militia to a standing army. They seem to believe that militias were raised voluntarily. Hey guys, if your father and brother were strapping on their guns you certainly had the freedom to develop a head cold and stay home. Provided you don't mind being labelled a coward, an outcast for life. Provided you don't mind a lifetime of humiliation and insults. Like being a dork in high school for the rest of your life. "Volunteers" knew that the risk of physical death was prefereable to the certainty of social death. Just as a "voluntary" militia system could only function in a society where shirkers are disgraced for life, so "choosing freely" depends upon a village society where reputations are in concrete and no one can sneeze without someone offering him a handkerchief.
But I don't think you need to be religious to be moral.
You cannot have a societal moral consensus strong enough to punish "victimless" offenses (like viewing pornography) without religion. In the absence of religion there are no hard and fast rules that anyone has any real right to punish or ostracize anyone for disobeying. The existentialists were absolutely right about that. No God, no moral rules.