Unfortunately, for a lot of people, many principles which were previously non-negotiable have become subordinate to short-sighted tribalism.

I'm not sure why that is, exactly, but a credible hypothesis might be that by living in filter bubbles, people simultaneously become less exposed to the shared humanity of their opponents, and also rewarded by their in-group for the "righteous anger" they express towards those opponents.

After all, if you're sure that your opponent is going to lie or cheat or kill you, then what's so bad about lying or cheating or killing them first? It may even feel like you're de-escalating the situation if you "only" censor people who you think are going to kill (someone like) you. (Don't get me wrong, some calls to violence definitely shouldn't be spread, but I think that people are too quick to justify their censorship that way).