I agree that it isn't really about 'left' or 'right', as both leanings are held by plenty of rational non-extreme people. Extremism itself seems to be growing in our culture, and as long as we're focused on putting a political label on it I think it will continue to grow. It is very tempting to believe that everyone you disagree with is part of the most extreme representation of that disagreement, because that makes it easy to dismiss them, and ultimately I think that just pushes people more to the extreme ends.

I don't know how we get out of this. I can't think of a good way to encourage empathy over outrage, as the former is often too painful and the latter often too enjoyable. In the information age it is far too easy to find the hedonistic outrage-dens, and there's a lot of money to be had running such places.

Speaking of likening echo chambers to opium dens, the Rat Park[0] experiments suggest that environment does play a significant role in drug-seeking behavior, and it does seem that a lot of this extremism can be traced back to things like the increasing wealth-gap, the hollowing out of rural America, systemic racism, rampant political corruption, and other societal ills. Therefore, maybe it isn't necessary to address the symptom of extremism directly --by, say, trying to teach people empathy-- but instead focus on treating the underlying illnesses. Of course, since our politicians are elected by the people they represent, and it would seem far easier to manipulate people's outrage for votes than to focus on actually fixing things, that might not be possible either.

[0] https://en.wikipedia.org/wiki/Rat_Park