Earlier quoted context omitted.
Horseshoe theory. Both the extreme left and the extreme right has reason to doubt/oppose the current political establishment.
The nice thing about extremists is that they're sufficiently non-invested in making the status quo look good that they're happy to point out when it's shit. Frankly I really like the extremists on both sides of the isle. While I might vehemently disagree with them on specifics they are at least generally principled people who derive their policy positions from their beliefs logically and I have respect for that.
Re your second paragraph: Things that logically derive from insane starting points can still be insane. Often are, in fact. When they are right, they are right only by random accident. I'm not saying "don't read them", but don't use what they say to adjust your priors very much.