It's a mistake to think echo chambers are a phenomenon which only take place on the political extremes. Reddit itself is an echo chamber of tepid liberal orthodoxy and American exceptionalism, moderated by a former member of the Atlantic Council. A fish doesn't recognize the water it swims in.

Redditors might call a place like Hexbear an echo chamber for instance, but it wasn't the members of Hexbear who chose to isolate themselves. Reddit made that decision by banning them.