>I'm convinced that a lot of people--probably even some of my own neighbors--wear a mask of civility only because we live in a society and have rules that are enforced. If the opportunity ever arrived and we entered some kind of Mad Max lawlessness, they would instantly start to murder and plunder just like barbarians out of fiction.

This is mostly a prepper fantasy that justifies things like buying a bunch of guns and canned beans instead of investing in more difficult things like community building. From the (IMO, naive) POV that human behavior is strictly selfish, it would rarely occurs that this kind of behavior would be beneficial to an individual's self-interest. Even in the worst-case, entirely imaginary SHTF complete destruction of society scenario, sociable behavior is more beneficial than any kind of anti-social Wasteland Raider behavior.

Maybe some aberrant individuals, but they would quickly fail without community support.

That preppers and the "tough on crime" set overlap is really curious to me, since in the first you have an acknowledgment that circumstances shape behavior utterly, and in the second you have people really, really eager to punish or deter on an individual level, rather than shape behavior by changing systems.

Lack of punishment is in itself an enviromental factor. I'm sure those people would love to hand out punishment themselves in non apocalyptic scenarios, but the law doesn't let them.