Has anyone pointed it out to him that he's got it reversed? What he's referring to as "America's vitriol" started getting really bad just after Wikipedia became a top-ten website. What he should be doing, and would be if he actually cared about history, is drawing logical inferences from the known (and well-documented) chain of recent events.
The fact is, Wikipedia does have a significant, though subtle and insidious, negative effect on political discourse in the United States. It's not direct; what it does is siphon off political moderates, attracted by the promise of "neutral point of view," and the false promise of artifical civility enforced by bans and such. These people might otherwise put in that time and effort to argue with extremist ideologues on other websites, if they really cared. Instead, they're told "don't feed the trolls," it's best to ignore the people who deal in "vitriol" and make irrational, or even violent, political statements online. In effect, they're fiddling while Rome burns.
This is all related to Wikipedia's Google footprint too, of course. (That sort of goes without saying!)
Anyway, the end-result is increased polarization and self-delusion - extremists thinking that the lack of opposition they see on their own blogs and news sites (and even their own encyclopedias) is actually evidence that everyone else agrees with them. Nobody blames Wikipedia for this because they're not deliberately trying to achieve this effect, but there probably isn't a better example anywhere on the internet of a site that does this.