I’ve heard a theory that Tarantino did all the gruesome stuff to the Nazis because they made him black-and-white that scene in Kill Bill. And something even worse was allowed to stay in color because of the beliefs of the target - basically the same mentality as the nazis.

Even if it’s not true it certainly points to humanity’s willingness for cruelty towards other tribes.

Here’s an article about how early homo sapiens are theorized to have caused a mass extinction event among other early humans.