It isn't about the First Amendment. It's about being rude and antagonistic simply for the sake of being rude and antagonistic.
Very trendy in acedemia nowadays, it seems. I guess it lets these professors sit at the "cool table".
But of course, being rude and antagonistic is only suitable for safe targets-- the right, the religious, and sometimes the Jews. Those guys will never sit at the "cool table" so it is safe to knock their books from their hands as pals point and laugh.
Ah, but that is the nature of acedemic thought... the depth of a dime but the width of an ocean.
Being rude and antagonistic is protected speech.