Because their entire poltical and world view is based on identity politics. They cannot simply say “that joke sucked” and move on, they have to make it into yet another virtue signalling exercise and lecture everyone else because that is the behaviour they associate with being a “good person”.
Totally agree with you in relation to groupthink and it’s the main reason I have them disabled too. I don’t like my opinion of a comment to be influenced by others before I’ve even finished reading it.