Who? I don't know of anyone who has even hinted this is true. It seems to me there is near universal agreement that the type of people currently known as the "alt-right" are always there, under their rocks. Trump's ascendance has encouraged many of them to come out and start publicly spreading their manure. But nobody alive during the last 8 years would make the mistake that these racist, sexist imbeciles are anything new. What's new is they are now gaining positions of greater influence. They used to, at most, be Representatives from the slave states.
No argument about this. One thing studying them will do, for example, is point out how ridiculous a comparison between them and South Park is, if for no other reason than South Park is satire whereas these losers are in deadly earnest.
Tiny amalgamations of people in the right lace at the right time can significantly change history. We ignore this cancer at our peril. And that's why I agree with you completely that rather than censoring them they should be invited to use all the rope they can get their hands on. No curse on them is as effective than merely quoting their own words.