It must really baffle you that Chomsky signed this letter.
And I have seen a lot of people on the left raising this problem and discussing how this will ultimately be used against them when, even when today it is done for mlre left-leaning goals. I think Professor Chomsky is extremely well aware of how easily tools of censorship are wielded against the voices of the minority.
And note that a lot of the grand-standing and calls to boycotts on these issues is coming from liberals, not leftists.