I feel you've drawn the wrong conclusion by inferring people are either good or evil. That's the Abrahamic indoctrination we receive in America because it gives us an "out". We are then allowed to think we are the good ones, which perpetuates the us vs them narrative.

More accurate is the understanding that all of us are capable of all things given the right circumstances. You get this after reading the rest of the "It Can Happen Here trilogy" - "They Thought They Were Free" and "Ordinary Men". We operate on tribalism, not morality. We are influenced by exposure, not absolutes. The pressure to conform is almost always stronger than our internalized sense of self.