Be careful when you talk about all of revisionist history like that. Much of it cleared away the hard feelings of the time that the previous history had been written in, but others took it too far, like what you said. The SS are a tricky subject not least because of their position in history. However, there is a rational explanation for their actions. First, empathy is not distributed equally, and so some people will naturally be more disposed to acts of exploitation, violence, even genocide than others. If you take that distribution and combine it with the distributions of those who were more active in the muscle side of the Nazi party and soldiers who had good track records in combat, you get a pretty good approximation of the criteria that described most SS members. Of course there were exceptions, such as the Jewish members, but every society has an 'SS' if you substitute any violent extremist organization for the Nazi party.
-Penguin