"This is outside our Overton Window!" - The media, probably

Right leaning papers do the same with the far-left.

That said extremists on either side can be pretty messed up if you start wishing violence on the "other side". That's how wars happen. Two groups of people, each convinced they're absolutely correct, each seeing the other as "obviously evil".

Extremists suck, but censorship sucks more. I might even go so far as to say that censorship creates extremists.