People are not evil
Everyone who was ever evil thought they were doing the right thing.
There's no such thing as an evil person. People who we now view as evil never thought they were being evil.
There's also no such thing as a good or a bad person. Everyone's a mixture of both, and we just want others to be good enough.
When you're doing something that you later realize is bad, you don't think "aw yeah I'm being so amazingly evil right now". No, you're just convinced that you're doing what you should be doing.
Everyone just acts on their values. So if you think someone's being evil, his values are what you should challenge.
That said, evil does exist. Some things are objectively bad. But people are not evil.
No one has all the information in the world to correctly judge whether their behavior is right or wrong. Everyone is just guessing based on what they believe.