Noam is on the short list of the most intellectually impactful human beings of the period since Descartes: Newton, Darwin, Smith, maybe Ricardo, Marx, maybe Frege or Russell, Einstein, Turing, Keynes, Chomsky, and a scant few more.
His politics may motivate people to disregard him, but mostly he's just come to the devastating conclusion (for solid reasons) that people working on language outside the Chomskyan tradition are not doing science; semantics, linguistic anthropology, and some areas of psychology are just wind. People who do such work will not understand his criticism because their academic standing depends on their not understanding it. There is thus a supply of motivated PhDs ready to dismiss and de-emphasize his contributions. Some of the same applies to philosophers who work on language.