Sam Harris wants to start a conversation that never get started with Noam Chomsky.
Noam Chomsky as a old man is quite dismissive of Sam Harris, who he probably considered as a minor character with no real importance.
And he would be correct. But that's does not make Noam Chomsky right in any sense.
My dislike of Noam Chomsky, especially on some of his political views is known only to myself. So, as a person who didn't see Noam as a "great", what I read is an angry old man who told off a person who dare to criticize him.
As for Sam Harris, his intention to engage in a dialogue is fine. But he is a bit naive that someone who is as arrogant as Noam would give him the light of day.
The best way to read this email, is to assign A and B to the character and read the email on its own before drawing a conclusion.
In that way, it is just a proof of a failed in communication. With that Noam had failed more because of his training.
To be fair, I didn't read any Noam Chomsky's work because I dislike authoritative tone in any writer. And now, I know for sure that I wasn't missing out.