[armchairhacker]

People get addicted to controversy and seeing someone else who is "wrong and proud". And when this happens, they start to make up their own controversy and become more radical in order to feed their addiction.

You can believe that you're "good" and define certain things as "bad" without being "self-righteous". Heck, you can pretty much be wrong about what's good and bad and still not be self-righteous.

The problem arises when your opinion becomes rigid and you stop accepting any debate, then when you broaden your opinion so that it becomes more radical, because you want to be "right" and see others be "wrong" so bad. And this can turn even the most reasonable opinion into something extreme, e.g. "black people deserve to live" turning into "white people don't deserve to live [because they endanger black people]"