I disagree. The small groups, especially the ones with self-amplifying „high echos“ in their groups are the ones (groups or individual members of that group) that easily radicalize. That‘s how terrorist cells, guerillas, and „lone wolf“ aggressors arise (left and right, political and social, agnostic and religious, whatever-you-can-think of extremists). Just check the news of the last months, I mean weeks…er, days!

And I‘m not saying your point about large echo chambers is wrong, it’s quite true (again, see recent news). But the problem is with any kind/size of echo chamber. And „echo chamber“ is a different thing than domain-specific groups like HN – it‘s only an echo chamber when HN is your only source of (tech/entrepreneurial) news/discussions. Note that even where you live can easily become an echo chamber if you rarely break out of it.