On the first criticism, often repeated, here is Chomsky himself, from 1983:
The foreign policy of other states is also in general horrifying -- roughly speaking, states are violent to the extent that they have the power to act in the interests of those with domestic power -- but there is not very much that I can do about it. It is, for example, easy enough for an American intellectual to write critical analyses of the behavior of the Soviet Union in Afghanistan and Eastern Europe (or in supporting the Argentine generals), but such efforts have little if any effect in modifying or reversing the actions of the U.S.S.R. Rather, such efforts, which are naturally much welcomed by those who dominate the ideological institutions here, may serve to contribute to the violence of the American state, by reinforcing the images of Soviet brutality (often accurate) that are used to frighten Americans into conformity and obedience. I do not suggest that this is a reason to avoid critical analysis of the U.S.S.R.; in fact, I have often written on the foreign policy of the Soviet state. Nor would I criticize someone who devotes much, even all his work to this task. But we should understand that the moral value of this work is at best very slight, where the moral value of an action is judged in terms of its human consequences. In fact, rather delicate judgments sometimes arise, for people who are committed to decent moral values. Suppose, for example, that some German intellectual chose in 1943 to write articles on terrible things done by Britain, or the U.S., or the Jews. What he wrote might be correct, but we would not be very much impressed.On the question of Chomsky's purported "support" of Pol Pot, Sharp points us in the direction of this article by Edward Herman, which is indeed quite good. Unfortunately, since Herman is closely associated with Chomsky, I fear that people might use that as a reason to dismiss his defense of Chomsky. (Chomsky & Herman co-wrote a handful of important books, including After the Cataclysm, the largely unread 1979 book in which they supposedly reveal their "support" of Pol Pot. Their Manufacturing Consent contains an entertaining application of their media model to this very "controversy".) So, while I do recommend Herman's piece as a decent place to start, I'd like to refer you to this excellent and comprehensive item over at Flagrency to Reason.
Attacks on Chomsky are depressingly common and similar. Some time ago, Brian Leiter wrote:
There's plenty to quarrel with Chomsky about (though at least he's worth quarreling with!). One could reasonably say, "I think Chomsky is wrong about X," or "The evidence really doesn't support Chomsky's claim about Y," and so on. But DeLong, and other Chomsky haters, aren't content with engaging Chomsky in argument: they have to establish that he is beyond the pale, that he is intellectually corrupt and dishonest, that it is no longer necessary to take him seriously.I don't know that I see "plenty to quarrel with Chomsky about"--I suppose it depends on how you define the word "plenty"--but Leiter is quite right. This is because, I think, his work directly challenges these people--intellectuals and the media and Liberals--and they find themselves unable to address it substantively, so they tend to ignore it and/or smear him. That intellectuals by and large are in the service of the state is a basic truism for Chomsky, not terribly surprising. Liberals like to hold on to the idea that America is good and means well and that its power could be used benignly, calling for this or that "humanitarian intervention", choosing to ignore extensive American culpability in those very regions ripe for intervention. And much of Chomsky's work, especially his work with Herman, focuses specifically on how the media reports on American policy and the ideological framework in which the media operates. And they explicitly use their propaganda model in the course of these studies. This is clearly not a legitimate area of inquiry. "[I]t is simply assumed that discussing the press is nothing more than cynical cover for some ulterior motive", as Josh Buermann wrote in the above-linked Flagrancy to Reason piece. Exactly so.
For a general clearinghouse of all kinds of complaints about Chomsky and how and why they do not hold up to scrutiny, please see this other, also excellent Flagrancy to Reason piece.