I completely agree. I study how groups of people interact. When working well, a group of people can tackle almost any problem. It's a magical thing to see.
Based on that, I experimented quite a bit with my blog, here on HN, and on various social platforms. Could that magic be reproduced online? Out of 1,000 or so online "friends", I have maybe 3 that consistently promote diversity of thought. Those people could moderate a room on about any topic. The people they gathered around them had all sorts of views and ways of thinking. It wasn't what I had seen in person, but it was the closest I've seen online.
So why not HN? Or FB? Or Twitter? Why did it work when some people ran/moderated discussions but not when others did?
There's too much to go into here, but one takeaway is that there was a system of incremental trust. New people we treat with kid gloves, see how they handle people who are smart and disagree with them. As we get to know you, everybody can relax more and have more direct, honest conversations. But when we did that, it was always full of things you wouldn't want copied and pasted to the public. Not bad things. Yikes! Just stuff that taken out of context would drive some folks nuts.
Online forums do not have that. So we're stuck desperately needing to meet and talk about complex and sometimes provocative things, but our tools are basically made for cat pictures and political memes. The social media services we have today simply are not in the public interest. There's no amount of tweaking that's going to fix that. They exist to serve base and lizard-brain impulses in various fashions.
One thing though. You're absolutely right about the dangers of echo chambers. But if you have an explicit small group, everybody knows what's going on. You know what's worse? Hell-banning, ghosting, and all of this damned AI trickery we do to one another to make people appear as if they are part of groups they are not actually part of. FB is getting so it'll stick you in that small echo chamber ... and you'll never know it. That's fucked up in more ways than one.