I believe the problem is how incredibly easy it is to both disseminate and consume utter bullshit. You're no longer that weird loner in town. You go online and can find hundreds and thousands of people who agree with you. Why would you go find people that challenge your views, when you can get those dopamine highs from people who love everything you say?
Get pushback from people in your life? Cut them out. They don't get you, and they're just hating.
The worst part? It's self-sustaining. Humans are really bad about going against a group. So much of our social behavior is around what others do, and the more we find out about others believing XYZ, we'll start to believe it ourselves. Unless they're from a different group, in which case it is anathema.
Combine those 2 things and you get these people who basically live in separate worlds. And social media/internet enables that.