Okay, here goes. This is all from personal experience, observation, knowledge, and um, use (i used to be a real shitheel when i was in the closet, go figure).
The basis of it all is that the modern fascists have figured out several logical traps that most people are ill equipped to deal with. Their behaviour and use of these can be likened to script kiddies trying out basic attacks on known weaknesses, only with human minds and culture instead of code.

The first is that everyone is taught that violence is wrong regardless. If you've been through school in the west, you know they punish people who strike back at bullies more severely than they punish bullies. Therefore, whenever anyone expresses disgust over fascist violence, they chime in with "rise above, be better, no antifascist violence" rhetoric, and will often spend time doing this just to spread that rhetoric.