I think you've made my point for me. If moral lines are easy enough to move that people will "shovel Jews into gas ovens and pull out people's fingernails," it's not hard to find people more than glad to cross class lines to enforce laws, whether those laws are just or corrupt (and most laws are in the middle).

At the core, there are few or no internal "Do Not Cross" moral lines. Moral lines are first culturally-situated, and second, individually-situated.

Incentive structures set by the ruling class drive a huge part of culture. Media does too. There are a lot of tools to manipulate culture, and they're actively (and increasingly scientifically) used. At the end of a Roman Triumph -- a big celebration -- captured war prisoners would be strangled in front of an audience. In that culture, that was okay.

From there, you need to find just a few people, either divided, disgruntled, or of low moral character. If I want to keep poor Southern whites in-line in 1870, I can find blacks who hate them. If I want to keep poor Southern blacks in-line, I find poor Southern whites. There, we had a nice 50/50 split, but there will always be a few.

The expectation that "it's the turncoats fault" isn't a productive one. You need to fix systems, not individuals (with incentive structures around individuals are part of systems, of course).

> I guess it just depends on where your internal "Do Not Cross" moral line lies.

As we've so often seen, at scale it's easy to move that line for enough people to enable any atrocity.

At the battle of Plataea during the Second Greco-Persian War, a number of Greek city-states fought on the Persian side. Why? Because the Persians were so big and powerful they were surely going to win.

The biggest trick the ruling classes pull is convincing those on the bottom rungs of society to always kick downwards.

Because the owning class have really good PR(you can also be like us if you just work hard enough) and can afford better physical segregation and legal protection against the working class.