They should be ashamed of their abominable deeds, but they are not. When it comes to settling differences, violence has been humanity's preferred court of last and ofttimes first resort.
Society discourages personal mayhem, but the collective violence of nations is another matter.
No one really wants it, but we expect war to happen occasionally. It is, after all, how governments settle their grievances. So we practice war, and because practice makes perfect, we've gotten really good at it. Innovations like poison gas and nuclear weapons attest to that. Our technical knowledge appears to have leapfrogged our wisdom.