who decides who the good guys are? if you get a good anthropology book, you'll find plenty of societies that value violence (to varying degrees). in fact, you don't even need an anthropology book, just open the old testament.
To me it seems self evident and non-controversial to all but the sneeriest of intellectuals, that some people are just bad.
Simple. Look at the guards at the border. Are they employed because people keep trying to sneak into the country, or out of it?