Hatred doesn't last long when you talk to people. But Facebook doesn't let people talk to each other across boundaries. It's segregatory. See Brown v. Board. Now, there is no middle, and we have a mess to clean up.
This maximized clicks. Facebook weren't the only ones doing it, but Facebook is the giant in the room. Facebook could have connected people on the left and on the right, and facilitated civil discussions. It chose not to do that.
Do I blame them for it? I'm not sure. Market forces are powerful, and I suspect its hand may have been forced. Nevertheless, it's something we need to fix. Regulation is nice since it changes market forces.
To say the polarized left isn't harmful is false. I don't much care about terrorists or bombers. There aren't enough of them to matter. I care about racists on the right. I care about vigilante doxers on the left. I care about people losing their careers. I care about kids from some communities not learning. I care about people hating each other. That's as much of a problem on each side.
There was an article I ran into earlier today about how the far left which just caused a USC professor to be suspended from teaching for saying 那个 in a course on communications (which sounds a lot like an American racial slur). This stuff happens all the time in the far left. Watch the video. What he said is exactly what you'll hear in China all the time.
https://reason.com/2020/09/03/usc-greg-patton-chinese-word-o...
As a footnote, if you do want to see terrorists on the left, tune into Fox News. They play nonstop footage of BLM protesters beating people up, setting fires, and in one case, executing someone. You can't just close your eyes here; half of America is seeing one reality, and half is seeing another. To start closing the gaps, it's helpful to see both.