While I don’t recall much off of the top of my head, some years ago I read something that the author described as the death of shame, which likely is a natural precursor to this loss of civility.
Classic, pre sexual revolution notions shame has been at every turn exorcized by the mavens of said revolution and the Left. And not just for things related to sex.
Inevitably in its place has come the effort to impose a new form of shame on any who do not conform to whatever the society seems to be doing at the moment, as was recently noted in another thread hereabouts where an otherwise card carrying radical feminist dared tweet that a woman is a biological female with and personality and not a “female personality” with any body.
What I’m describing is an irrational process for many, hyper-conformity where the side with the loudest angriest bullies gets the unwavering cowardly support from people who use virtue signaling in hopes of being unmolested ... and as a result are often eager bullies themselves.
Which is why I’ve taken to comparing the Left for which there remains no part of the old extreme Left that’s extreme to them anymore to a proverbial flock of angry and canabalistic birds.
These birds sing (virtue signaling etc) not to find a mate or acquire / defend territory but to announce that they conform to the flock, and they eagerly tear into any bird that lets its song deviate too far from whatever the flock is doing at the moment.
Of course it goes without saying that these unwholesome and hyper-conformist brutes are not nice to any people / other critters outside of their flock.