You don’t need to. The target audience was people to whom that’s obvious in the first few lines and then who keep reading to see how far he can take it with a straight face.
Yes, he was “joking”- he is what the Internet calls a “Schrödinger's dbag,” it was only a joke if people don’t agree, but if they do it’s what he really believes- a cowardly way of communicating. In the context of his career, his actual beliefs are along the lines of the essay.