The Khmer Rouge justified its violence by claiming it was wiping out the urban bourgeoisie and that this was a necessary use of force whose purpose was to achieve a more just society. In other words, the people they killed deserved it. Chomsky may have bought this argument. He certainly hasn’t shied away from it in other cases.
Remember, in terms of motive what the Khmer Rouge did wasn’t hugely different from what most other radical Left regimes have done when they seized power. The major difference is one of scale. That is, in terms of the number of people dead and especially in terms of the percentage of the population that was annihilated, the Khmer Rouge was disproportionately bloodthirsty…
In a certain sense Chomsky was a bit late to the game on Israel, though he more than made up for it afterwards. It didn’t begin with him.
The New Left was already moving against Israel as far back as the mid-1960s. It really starts with the Suez War in 1956, when Israel turns decisively against the USSR and pivots toward the West. The Soviets started pumping out the anti-Israel propaganda, and people in the Western Left naturally started falling into line. And certainly, the rise of a certain kind of Third World-ism that fetishized the Arab war against Israel predated Chomsky’s emergence as a major voice on the anti-Israel Left.
It’s also important to remember that, despite Chomsky’s intense hatred of Israel, his real idee fixe has always been the United States. It’s only as Israel starts to draw closer to the US following the Six Day War, and especially after the Yom Kippur War, that he really gets going.
It’s for this reason that the question of his remaining pro-Israel really isn’t a question at all. As soon as Israel became an important ally of the United States, Chomsky could never have been pro-Israel even if he’d wanted to be. It would have thrown his entire worldview into disarray.
I would say, though, that he solidified the position of the Left on Israel and certainly gave it a lot of ammunition. He also played an important role in giving anti-Israel ideas a legitimate place in the American intellectual debate—especially in academia—and in making it a sort of litmus test for Jewish Leftists.
A lot of the things he wrote in the wake of the Six Day War were denunciations of fellow Jewish Leftists for not being “real” Leftists because of their Zionism. So as a collaborator in what was basically a purge, and in ensuring that Jewish Leftists knew that the price of their continued participation in the movement was their support for Israel, he did play an essential part.
He was also one of the anti-Israel Left’s first and probably most important shields against accusations of Anti-Semitism. Since he was one of the most prominent Jewish intellectuals in America at the time (mainly for his linguistics work), he gave the anti-Israel Left a lot of cover, and allowed them to escape responsibility for the Anti-Semitic aspects of their ideology for a long time.