“If only it were all so simple! If only there were evil people somewhere insidiously committing evil deeds, and it were necessary only to separate them from the rest of us and destroy them. But the line dividing good and evil cuts through the heart of every human being. And who is willing to destroy a piece of his own heart?”
― Aleksandr Solzhenitsyn, The Gulag Archipelago 1918-1956
Jordan Peterson talks about how one of the most important things you can do to become a well-formed person in terms of moral reasoning is to realize that you're a Nazi. You're a concentration camp guard. You'd do it, by choice. It takes a lot of discussion and examples and thought to get to the point where this is really understood, but it's true and it's important.
I'd say the main thing that convinced me is that I realized that there are people I'd like to see suffer. Not because it'd lead to some external outcome, but just because I want them to suffer. You can see this every day in politics too. People who want to hurt just for the joy of hurting. You can hear it in their voices when they knock people down at a protest and hurl dehumanizing snarl terms at them.
And this is present on every 'side'. The only possible difference is in how much each side embraces this impulse.
Once this is understood - that people aren't divided into good and evil groups, but rather that every person is both good and evil - a lot of questions and problems look quite different from the common "good people vs evil people" frame. A lot of policies and historical judgments start to look pretty dumb.
And, in fact, the idea that some people are evil is a foundation of evil acts. The false belief that someone is pure evil is what gives you the excuse to feel good about making them suffer.
It's ironic that wrong beliefs about the shape of evil in the world are themselves a foundation for evil.