Except its millions of times bigger in its scope and reach. That makes it qualitatively a different thing entirely

> Exactly. Facebook isn't dramatically different than your local pub, church, Elks lodge, knitting club, or any other self-selected social group. Singling them out and treating it like a new problem gives too much credence to the notion that it's a new thing.

No. Facebook (and web echo chambers in general) are dramatically different. Because the available online population is so much larger than a physical community, narrower and louder echo chambers are possible. Back in the offline days echo chambers were more self-limited and internally more diverse, because the smaller pool of possible members meant too much exclusion would make the group too small to be sustainable. Now, every crazy fringe idea can have a Facebook group of 500 active members egging each other on, and use targeted ads to easily suck in every susceptible person.