One of the points brought up in the article that I think is becoming pernicious is dicrediting by association. Any view that is also positively regarded by an extremist group (right or left) becomes evidence of the author's support for that group, even though there is no connection between the two. That's kind of like saying Apple must have created iPhones for criminals because they're preferred by drug dealers for their privacy! It would be nice if ideas could be judged on their own merit, not by who likes them.