The Ox-Bow Incident (1943) is a bleak but very impressive western about the problems of posses and mob justice – it’s Clint Eastwood’s favourite film and a remarkable early riposte to myths about the Old West.
If you fancy something slightly less depressing, Eastwood made a film in 1968 called ‘Hang ‘Em High’ which is a bit more of a romp, but still makes some serious points about why the mob and the death penalty is bad. There’s a scene where a bunch of criminals are hanged essentially as a piece of entertainment which really hammers the point home. I’ve strayed a bit off the point here, but I like movies. Sometimes, I just talk about them.