Humans have always killed to the maximum extent allowed by the technology of the time. It's perfectly natural, whether you're a Roman massacring the population of Carthage, a German gassing Jews or an American dropping an atomic bomb.
Whether they are "evil" or not depends solely on the point of view of the observer. At different points in history certain people have believed all the above acts were justified and necessary. Certainly nowadays the overwhelming view is that the holocaust was evil, and there is a growing voice that claim the use of nuclear weapons on Japan was wrong.
Personally, I think humans are all inherently evil. We only do things for our own selfish ends whether we do it overtly (snatching an old lady's handbag) or camoflagued as social good (XR, demanding that all follow their idea of the direction the future should head in).