John Cleese defines extremists (and thereby explains social justice warriors and "tone policing")

The biggest advantage of extremism is that it makes you feel GOOD because it provides you with enemies. Let me explain. The great thing about having enemies is that you can pretend that all the badness in the whole world is in your enemies, and all the goodness in the whole world is in YOU. Attractive, isn't it? So, if you have a lot of anger and resentment in you anyway and you therefore