Social media definitely did it. It's easier to draw tribal lines and fully demonize those you disagree with when you don't have to see their faces or sit in the same room as them. Where you can say whatever you want to them or about them in your echo chamber without fear of retaliation (be that verbal or physical), and if you do get any, you can just cry to an online nanny to ban the offender. Where you won't ever find a time where you'll have to rely on them, whether that be to help you with work, an assignment, or just for a cup of sugar, and thus have no need to learn to play nice. And where, after getting exposed to the worst extremists online, you start to paint everyone who bears similar but lesser or moderate beliefs with the same brush, which causes your treatment of people online to spill out into the real world.