You are the one making a positive claim that Chomsky has done something. I can't prove the negative, therefore the burden of proof is on you.
"The necessity of proof always lies with the person who lays charges"
If by "factually deficient" you mean false, then that is the definition of misinformation. Which is of course separate from disinformation, which is when you do that purposefully.
On the contrary, if you wish to learn about Chomsky's views towards the Khmer Rouge, the onus is entirely on you to investigate Chomsky's work. Failing that you're entirely at the mercy of intermediated secondary sources of indeterminate levels of trustworthiness, including myself.
Considering the nuanced nature of the claim - a conclusion as to his sympathies borne of deep familiarly with his work - there's no reason for me to think you wouldn't find additional reasons to quibble over any specific citations and passages. I have no evidence that you're a good faith interlocutor, so I really see no reason to expend that effort. If you're actually interested, I do encourage you to read the original works. (If it wakes you up to Chomsky's sympathies and immunises you against some of his bad politics, perhaps not a total waste of time.)
Look, you are making a claim without evidence. One which I know has been peddled by right-wing propagandists, who have put words into Chomsky's mouth (e.g. David Horowitz).
Therefore, without further clarification, I must assume that when you say "Chomsky backed the Khmer rouge", this is what you meant.
The burden of proof is on you. And if you are (as you say) so familiar with Chomsky's work, and if his sympathies with the Khmer rouge are "pretty clear", you should have no issue actually producing the "pretty clear" statements to this effect.
If anyone is asking someone else to do their homework for them, it's you. You made the claim, not me.
The disconnect here is that I have a degree in polsci and have read much of Chomsky, and you're repeating a "debunking" (replete with declarations of "fallacies") in a manner that is popular with people whose level of familiarity with political science is "I am active on Reddit".
"Therefore, without further clarification, I must assume" (what a mouthful!) that you are an argumentative teen with a "debate me bro" mindset.
One of the key problems of online exchange is that it is impossible to synthetise expertise without someone much less knowledgeable driving by, and demanding ELI5 level proof. They believe that they must be capable of reaching the same conclusion as someone who has spent years on the topic, and they must get it now, and they firmly believe that the onus is on the expert to give it to them (for some reason). The implication being that years of familiarity are irrelevant unless you replace your nuanced point with "pan in the face"-level direct evidence, such as would satisfy the "debate me bro" teenager who is demanding it. All expertise is invalid except that which an inexperienced Redditor can see with his own eyes (an obvious parallel exists here to conspiracists who "do their own research").
Consider that it would be relatively trivial for me to just type "Chomsky khmer rouge" into Google and throw some random refs at you, and that there may be some reason I haven't done so.
It is both (a) pointless - in that I truly do not care one jot if I have provided a satisfying level of evidence to you (and what about the next Redditor that comes along? and the next one? are we to be stuck at this level of discourse forever?), and (b) fairly deleterious to discussion that happens at a level more sophisticated than first principles.
Consider the implications for the progress of society of being forever stuck in ELI5 performative debate for the benefit of random lay people. The FOX News-ification of all of academia. The reduction of all human knowledge to that which is digestible to the average Redditor.
I note also your reference to right-wing propaganda, etc. From an academic perspective, this is just such an irrelevance. I am not a Marxist, for example, but I find Marxism to offer an occasionally useful lens on economic power relations. If you're still indulging in partisan "he says she says", then I respectfully do not think we're operating at the same level on this topic. That's not to diminish your intellect or knowledge in other fields. I'm sure there are many other skills you have that I do not.
You are entirely free to walk away completely confident you're right and I'm wrong, and this is something that will never matter to me in any way for the rest of my life (I will forget that this exchange ever happened within days). I suppose I engage only in the (probably vain) hope that I might plant a seed in you or someone reading this. I'd consider you going back to read Chomsky a win here, even if I disagree with a lot of his conclusions, because at least there's more to him than this "debate me bro" hellscape.
I won't reply again - this is not a good use of my time. Up to you whether you choose to interpret that as a win (epic Redditor destroys boring academic with facts and logic!) or an opportunity for contemplation.
Look at how much energy you're using to not give a reference for something you're claiming.
I'm asking for one (1) source where he is "pretty clear" about his Khmer rouge sympathies. You are writing up a storm to make that seem like an unreasonable thing.
And you would start this exercise by googling "chomsky khmer rouge"? Implying you have no mental model about what Chomsky said and when. Strange, considering your posturing about your political science degree and familiarity with Chomsky's work.
I must assume you have a PhD (or that you're working towards one), because you call yourself an academic. Any decent researcher would be able to identify sources for something they claim to be an expert on. At least, that is my experience, having worked in academia for a while. But you can't tell me what Chomsky said or where, even in broad terms?
"The necessity of proof always lies with the person who lays charges"
If by "factually deficient" you mean false, then that is the definition of misinformation. Which is of course separate from disinformation, which is when you do that purposefully.