> More decentralization is a recipe to spiral further and further into fragmented echo chambers with their own self-reinforcing ideologies and their own alternative facts.

Except the problem possibly isn't decentralized, separate echo chambers, it's centralized, connected echo chambers. Facebook was a single source through which you could easily find your echo chamber of choice, with a standard interface, no need to login or commit to anything, but you could easily find and follow the type of content you like.

If instead each echo chamber needed to set up its own site, with its own sign up and follow process, you weed out a lot of the fast and easy paths to disseminating bad information.