I agree that his contributions to proto-computer-science were real and significant, though I think they're also overstated. Note the link to the Wikipedia page for BNF elsewhere in these comments. There's no evidence that Backus or Naur were aware of Chomsky's ideas vs. simply reinventing them, and Knuth argues that an ancient Indian Sanskrit grammarian deserves priority anyways.

I think Chomsky's political views were pretty terrible, especially before 1990. He spoke favorably of the Khmer Rouge. He dismissed "Murder of a Gentle Land", one of the first Western reports of their mass killing, as a "third rate propaganda tract". As the killing became impossible to completely deny, he downplayed its scale. Concern for human rights in distant lands tends to be a left-leaning concept in the West, but Chomsky's influence neutralized that here. This contributed significantly to the West's indifference, and the killing continued. (The Vietnamese communists ultimately stopped it.)

Anyone who thinks Chomsky had good political ideas should read the opinions of Westerners in Cambodia during that time. I'm not saying he didn't have other good ideas; but how many good ideas does it take to offset 1.5-2M deaths?