These people killed others because they felt that they were a higher life form having evolved in a much superior manner than the ones that they were oppressing. And since they abandoned all moral absolutes as most Evilutionst do, it is a natural course of events. I believe you call it "survival of the fittest". These tyrants believed that they were eliminating a lesser element of the gene pool and thus serving a higher purpose of mankind and of it's ultimate survival. That is where evolution ultimately leads. Man justifies his baser urges for he deduces that it is only part of an engrained desire for survival by eliminating a lesser life form. Evolution, ultimately leads to anarchy and subjection of the strong over what is preceived as the weak. Ironic isn't it. You think that you are evolving but in actuality you are de-evolving morally. All leading to self destruction. That's why we need a saviour.