The Guardian has a well done podcast episode about Hannah Arendt’s ideas about the banality of evil. It includes a good summary of Milgram’s research, and the implications for the banality hypothesis. The consensus seems to be that banality isn’t really at play in genocide, but rather that there is real mindful action happening.
But, what happens when the situation around you is so infused with behaviors that are tantamount to evil? That the normal response is to kill and maim? Do you mindfully or mindlessly go along? Questions like these are why I like being a social psychologist.