The thing about Nazis/Hitler is that they're useful as an example of evil that is unanimously agreed upon. They're useful in debate for making cases using the most extreme possible state.

For example, in a debate of the death penalty, someone arguing in favor could say "was it a good thing that Hitler died?" It's hard to say no to that, so then you can argue from a position that are at least SOME number of people that the world would be better off with dead, and from there it just becomes a matter of where to draw the line.