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.
That's what scared me the most of all the stories on WWII, I could have been on the bad side just as easy. Once you are forced through the threshold of decency there is no holding back.
Having lived in a place with a "Durchgangslager" history, knowing that concentration camp had been built by the Dutch, before the war, did not make my view on the good of people more optimistic.
Yet, almost every day, I also see things that are just kind, and good, without any reward as an incentive happening.
People do have both in them indeed.