Isn't the necessary conclusion then that we are necessarily "progressing" towards "more good"?

Chomsky says we have "penetrated more deeply into our ACTUAL moral values". It's unsubstantiated and an unnecessary assumption. It seems to me that quite possibly the issue of subjective vs objective morality is either a confusion of terms (in what ways can valuations be objective and in what ways can they not?), or else an argument similar to determinism vs free will. Unfalsifiable and thus not worth considering EXCEPT as a means of realizing that our moral values are not fixed and so there may be some possibility of having a degree of agency in shaping them (individually AND culturally).

I mean, chomsky in his argument continually relies upon current and past moral standards, but that ignores the underlying value(s) - the actual criteria. If yesterday you asserted "the world is flat" and tomorrow you asserted "The world is round" and chomsky came by and said "See? Science progresses towards truth!" without FIRST establishing whether or not the world is actually round, then he hasn't made the point he thinks he has. And that is what he is doing with morality. He is saying "Moral standard 'y' went to moral standard 'z', therefore morality is objective" without actually establishing the latter. All he has pointed to is change.

You could more easily conclude that because morality is in part mimetic, we are at an elevated risk of believing our current moral values are the "most good" and thus we are in a perpetual motion toward "more good". That seems to me to be nothing but dogmatism.