What's scary is that the same people can be guilty of both
Nazis who could be incredibly sadistic or overlook the most awful crimes against humanity, can at the same time be kind, generous and sensitive people in another situation. Usually depending on the person involved. A lot of Nazis involved in the holocaust or related violence would have been good, decent family men who were liked by their community and would have done just what that teenage girl did on 7/7 - but then in a different environment, and more importantly when faced with a different type of person, they're capable of either taking part in or overlooking the second kind of behaviour.
It's mostly down to dehumanising people. The Nazis didn't view the Jews/Slavs as people like themselves. They were Untermenschen. Subhuman. Lower than dogs. So to them, how is making a lampshade out of human skin any different to a woman who wears a fur coat? That;s how it would be seemed to them.
A good example of this is stories of German soldiers in the East being completely oblivious to Russian peasants seeing them naked or even taking a shit in view of them. Obviously that's an extreme example, but it happened because they didn;t see them as people. In the same way that most of us wouldn't be embarrassed by a pet walking in on us in the same way we would another person
That's what's fucked up about thiese things. We're all capable of good and bad, and no matter what views/beliefs you have, no matter what type of person you are in this life, you can never truly now how you would have acted in a different environment. I often think about that. Who in my neighourhood would be the ones spitting on the [Jews] in the street, and who would be the one to risk their lives hiding someone in their loft? There's no way of knowing. We all like to think we'd at the very least not ACTIVELY take part in the persecution of the [Jews] if we'd been there. But the fact is that the percentage of people who wouldn't is much lower than the % of people who like to THINK they wouldn't.
Think of all the 18-40 "Aryan" men you know. Most of them would have been in uniform in some way. Some would have been in the police or the SS. There's no way for us to know how we would have behaved