Echo chambers have always existed... we all used to live in our small little world, with our small number of friends and family, talking about the same small bullshit.

The thing the internet gave us is anonymity. People are much less careful with their words or how insulting they are when they know there aren't repercussions. People also tend to assume a lot about someone based on one argument of view. A simple loaded phrase can have people calling you a racist, having one view can lead people to lump you in with other much more extreme views, even defending moderate positions can force people into more extreme positions because people hate losing any ground in an argument. So you'll have a libertarian who was moderate suddenly thinking social darwinism ain't such a bad thing after all. A conservative becomes a racist because they have views that are deemed not quite kosher, and if they have to be a racist to have views that seem perfectly reasonable to them, well so be it, go all the way. A progressive is a freeloading hippy even while they work their ass off, and if they're a hippy while working that hard, then maybe they should be demanding free shit cause they're getting nowhere on their own.

It's mob mentality on a global scale.