This sort of thing infuriates me because it's simply a lie - representing one cooky course at one famously non-traditional SLAC as typical! - and Rich Lowry (the author) knows it is a lie he is cravenly telling for political advantage. If your ideas are good, you don't need to lie.
They also have a farcical idea of history education. I bet there aren’t more than a handful of profs in the whole country who still use Zinn as a primary text. They are more likely to use him to illustrate changing historiographical interpretations and the intersection of politics and history.