The issue isn't if Chomsky's credibility is relevant, but on the credibility swipe itself: If Chomsky can be dismissed on all topics (zero credibility on anything) for alleged genocide denial, why isn't that "rhetoric that ignores X" for whatever X Chomsky might discuss?
I was dismissing Chomsky's testimony on anything, not anything he might say. If he said '2+2=4' that would be true (if also trivial). I regret not being 100% clear in a forum comment.
Because the only source given for the quote was Chomsky himself*. In that case, the question of Chomsky's credibility is directly relevant.
* It's possible Chomsky had an actual source etc., but if so, it was not provided in the original comment.