Chomsky already was very active and well-known by 1960.
He pioneered areas in Computer Science, before Computer Science was a formal field, that we still use today.
His political views haven't changed much, but they were beneficial back when America was more naive. They are harmful now only because we suffer from an absurd excess of cynicism.*
How would you feel about Chomsky and his influence if we ignored everything past 1990 (two years after Manufacturing Consent)?
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* Just imagine if Nixon had been president in today's environment... the public would say "the tapes are a forgery!" or "why would I believe establishment shills like Woodward and Bernstein?" Too much skepticism is as bad as too little.