I wonder how much of the "polarization" in the last two decades is simply that TV and music and media consumption in general became a personal and not a social thing with phones laptops etc, so you no longer have the various forms of social coercion pulling everyone to a cohesive illusory center when they overhear you straying from the path. (this isn't inherently good, to be clear)
even books have covers everyone around you sees, kindles don't
