Hitler actually thought he was saving his people from the Jews and the rest of the world who would kick around the German people. He thought it was a just course of action and most of the country followed. In Vietnam, perfectly normal men who should have led perfectly normal lives were killing others and destroying homes. They were in self-defense mode. They felt threatened and it justified their actions to them.
Man is inherently good.
Man has a natural instinct to help and do the right thing. Evil is seeded and grown when combined with a survival instinct. Evil replaces fear. I know it's a dream. Hopes and dreams are the only things that get me up in the morning, these days.