> and when "anybody who thinks that it's okay for there to be consequences for racism / sexism / other bigotry is a worthless California leftist and should be ignored" became the default modus operandi of many right-wing extremists.

That was always the MO of right-wing extremists. But after Trump's election is when people whose views were once considered moderate-left to moderate-right suddenly became "far-right", "alt-right", or "Nazis".

I think it stems from a mentality that someone else pointed out: not wanting to discuss the matter is tacit support for the status quo. A.k.a. "if you aren't part of the solution, you're part of the problem." A.k.a. "Until they are free they are part of the System, and that System is the enemy." If you aren't anti-racist or anti-sexist enough, you must be racist or sexist.