But insulting people is also degrading the quality of discussion. More so than just asking “bad” questions.
Subjectively, I agree, but not everyone shares that perspective, otherwise you wouldn't continue to see the typical "Genius but angry FOSS developer" personality in various communities. No one wakes up in the morning and decides to be an asshole, obviously they think they're contributing/adding more than they destroy, hence the continued behavior.
That makes sense if they're just visiting the channel sometimes. But I'm guessing they saw themselves as somewhat responsible for the community and quality of discussion in the channel, and then just walking away isn't really a solution.