You may recall the advice about waiting til next morning to hit send on that scathing email reply. You might not feel so dramatic after a cooldown period.
My working theory on why Twitter is so noxious is that it captures (then broadcasts) people's impulsiveness reaction.
I keep thinking of Marshal McLuhan's The Medium is the Message. What would he say about Twitter?
I've never grokked McLuhan's distinction between "hot" and "cold" mediums. (Makes sense; being one of the first to discuss this stuff, he had to invent a vocabulary.)
My current guess involves feedback loops and channel bandwidth. "Hot" is reactive, "cold" is deliberative. But it's not just the immediacy of the medium, it's also the interactions (feedback loops).
Face to face, there is very high bandwidth (included by not limited to backchannel, body language, facial expressions, context, etc) along with rapid feedback. So we have the information needed to keep communication from going off the rails.
Alas, Twitter's very constrained bandwidth, while maintaining the rapid feedback loop, doesn't permit any sort collaborative moderating effort.
In other words, Twitter is custom built for kneejerk clapbacks.
For contrast, I keep thinking of John Carmack's journaling via a .plan file (and the finger protocol). Twas a precursor to blogging and RSS feeds. Why didn't that medium incite virality, outrage, and pogroms? .plan files are also low band width, right? I think it's because the feedback loops simply didn't exist.
If you were just with one other programming friend, you might make reference to a repo you'd seen and say something like "yeah that approach is totally batshit", but you wouldn't say the same thing to the author in a public forum in front of many people. I think Twitter tricks our minds into behaving like the former but actually in the latter. So it's easy to forget that you may as well be directly insulting the author.
His analogy, IIRC: teens treat social media as hanging out at the food court with friends, not as public speech. To them, adults eavesdropping are the creeps, not the kids just being kids. Like, why would adults even be listening? It's just gross.
Corollary: privately, most people really are assholes (and they just suppress it when they don't feel bold/secure enough to be open about it)?
A good simple example is the way people tend to tidy their house before having guests. The cleanliness isn't "false" by most people's view.
Edit: Another perspective is that people use the company of trusted friends as a staging area for shaping their own nuanced positions. It's safer.