>We did just fine associating with people of different political perspectives and discussing politics with them all the way up through 2008 at least, without the violence.
You must have forgotten the US Civil War, plus all the turbulence of the 1960s.
The big difference there was that, for the most part, the two sides were geographically separated from each other.
>The complete refusal to interact with someone who disagrees with you is a relatively new phenomenon that seems to have risen alongside social media.
If you're thinking of the early-to-mid 20th century, things have changed. America has become much more diverse, and co-mingled (in the past, immigrant and other minority groups tended to keep to themselves and not socially interact so much with other groups). White European-descended people are no longer the overwhelming majority (remember, immigrants in the past mostly came from Europe), religion has lost much of its power and many of its believers, homosexuality has become far more accepted, basically one side feels existentially threatened, and the other side oppressed.
