The Popper part is easy: In the 1970s, during the student revolts, many right leaning people (who would be called fascists these days) got platforms on talk shows and politely debated their left wing counterparts.

It did not lead to the Fourth Reich, on the contrary, public opinion has shifted to the left in and after the 70s.

The right wing backlash you see now is a direct result of the insanity and totalitarianism of today's "left", which is really a smoke screen for the corporate-directed suppression of the middle classes (both black and white).

This Popper statement, made in a completely different era, is overused to shut down opponents and justify censorship.