One of his most interesting scenes in the film has him point out how people estimate horrible things differently depending on whether they're part of what's "normal", what's "expected", rather than on how inherently horrifying they are, or how many people are involved.

Agreed. I love that scene!

Soon people extrapolated this observation to other such apparent inconsistencies in human judgment, where a behaviour that once was acceptable, with a simple tweak or change in context, becomes the subject of a much more serious reaction.

Indeed. The social psychology experiment about people asking to cut in line with/without a reason is a good example.

I intuit that there's some sort of underlying pattern to them

Check out Thinking Fast and Slow. If I understand you correctly, you're referring to heuristics and biases, which have been studied pretty extensively. I apologize if you're already aware of this and I'm missing your point.