The ruffling seems to come from the term: universal grammar. Without a proper understanding the term can cause all sorts of misapprehensions. It sounds like a mandate; it makes people rebellious. Noam Chomsky specifically disavows any evolutionary theory. He just hand waves it for the establishment of the model. Many people who "refute" him simply attempt to provide this. All he intended to build was the simplest concievable system for language parsing. That's all he ever claims to have. When he responds to criticism it is always staunchly from this context. People just don't care to understand the propositions of the actual idea. I suspect they're intent on invalidating him to undermine his political views.
Many -- perhaps even most -- of his fiercest opponents within linguistics agree strongly with most of his political views. George Lakoff, for example, is well known as a leading anti-Chomskyite linguist, and also as a vocal far-leftist whose political views largely echo Chomsky's.
I'm not so sure that it's correct to call Chomsky a leftist. He clearly is not a Marxist and finds the ideology ridiculous, at the same level as religion. If Lakoff is a Marxist or socialist, then the two clearly do not have political views that are compatible.
Chomsky is, I believe, best referred to as a social libertarian, which means that he opposes both state and enterprise power and see them as more or less the same, and instead favors the individual. It is clear here why Marxists don't like him, at all.
I think this is also why the authors of the OA challenge Chomsky without offering anything other than minor claims hidden away throughout the text that language is a product of social interaction rather than a capability that lies within the individual. It is about the collective versus the individual and as a fierce individualist, the authors disagree with Chomsky on political grounds, not scientific.
Not all leftists are Marxists, though they have come to dominate the field. The broad anti-capitalism of anarcho-syndicalism, combined with his well known criticisms of American and western power for so called imperialism, definitely slot him into the "leftist" category in my political schema.
