Killing is not quick and painless. It is long, and drawn-out, and filled with despair.
Nature is not nice. Nature doesn't care for feelings or pain or empathy. So that's why I get so angry with anyone who tries to explain cruelty or the abuse of power by pointing out that people are just being true to their animal nature.
Well, isn't that what being human is all about? Rising above our animal nature?
That's the definition of greatness, to me. Not the willingness to kill, which is easy. But the willingness to talk and negotiate and see the humanity in our fellow humans, and even in our fellow Earthlings. To deal with others with respect. The same respect we require from them.