I will do my best to stick with fallacies here, as this is what this site is about.
As you probably know, many 9/11 truthers point out that the 9/11 terrorist attacks helped George Bush's administration, the military-industrial complex, the corporate sector, the United States' allies, etc. It doesn't prove anything, but it is a key piece of evidence that 9/11 was an inside job - a so-called "false flag attack."
This is a good example of the Ad Hominem Circumstantial Fallacy, or would be depending on how significantly this is weighed as evidence. For example, when my mom died, I got about $100 worth of her stuff. This isn't evidence that I killed her. Through the confirmation bias , one may only pay attention to the benefits and ignore (consciously or subconsciously) the great costs. Also, we should distinguish between evidence for motive vs. evidence for the crime. For example, if Trump were murdered, roughly 60% of Americans would have motive. In no way is this evidence that any of them committed the crime.
Chomsky's "argument" that the government's response to 9/11 was PREDICTABLE, therefore, it could not have been an since [sic] job, is ridiculous.
Had Chomsky stated this or even indirectly implied it, it would be an example of a non-sequiter . It doesn't follow that predictability validates or invalidates the conspiracy.
I have not watched the video, but I would be really surprised that someone of Chomsky's intelligence and experience would say or even imply such an argument. He may have, or you may be creating a strawman of his position. It is difficult when one does not have the opportunity to ask questions (i.e., "Noam, are you saying that because it was predictable it couldn't have been an inside job???"). In absence of clear information, we tend to support the interpretation that supports our position. So perhaps the best we can say is "we don't know what Chomsky meant exactly".