In the old days a person with radical ideas had a hard time finding others with the same mentality. It cost money to send out letters, print stuff, etc. Now you can blast out whatever comes into your head to potentially millions of people. You an form groups with them and feed each other’s paranoia and biases. On top of it broadcasting to you has become even easier and targeted.

Then there is the whole issue of the “anonymous asshole” online who feels disconnected to those they are communicating to and makes assumptions (usually hostile) about them and feels freer to be hostile or provocative.