Good addition, and also a good example, because that was so common I didn’t even recognize it as a problem. I’m still unlearning a lot.
If a post/comment is sufficiently stupid, the stupidity is obvious and speaks for itself. I leave it alone. Of course, bigotry and hate speech can’t be tolerated and should be called out (plus reported, because Nazis and bigots can kiss my ass), but otherwise, I just ignore it and move on. In most cases, I think we help quite a bit by setting the tone and not arguing. As people see that negativity isn’t the norm, they’ll gradually change.