Chomsky’s position is that the burden of proof is on state violence to justify itself, and I think he would agree it’s clearly justified in that case.

However, that’s a very narrowly scoped restriction (and it’s also not clear that such distribution is a type of “speech”). A more appropriate question would be: would Chomsky support free speech for an advocacy group such as NAMBLA, or for creating mangas that depict drawings similar to CP? Those are exactly the type of speech/expression that are clearly vile, yet should still be protected from interference by state violence, from the civil-libertarian perspective.