I have no love for postmodernism, but this seems at least mildly unfair. Sokal's initiating action was entirely political. Responding by saying that Sokal hurt himself more than anyone else is a decent strategy, and might be true too, but it's not a symptom of postmodernism.
Claiming that people outside a field don't understand is a symptom of academics, and of most groups of humans, but it is not something in any way unique to postmodernism.
Whether or not his action was political, their response that insinuates that he is not a true leftist is not only incorrect but irrelevant, though it's understandable that somebody in a field where virtue signalling is so critical might think that this is a valid counterargument. Imagine that somebody pointed out that articles in a mathematical journal are incorrect and the editor responds with "yea, but you're not a true leftist!!". Virtue signalling and victimology over arguments, opinion over facts, obscurantism over clarity, etcetera.
The claim that people outside of the field have a hard time understanding it has the advantage of being correct when applied to science and mathematics. This is why Sokal's book only analyses the use of physics and mathematics in postmodernist literature. Since he is physicist and mathematician the claim that he just doesn't understand what he is talking about in his criticism falls flat.
I know I'm being harsh, but ridicule and contempt is the only way to get rid of this before it further infects campuses and, after the current generation of students grows up, politics.
Claiming that people outside a field don't understand is a symptom of academics, and of most groups of humans, but it is not something in any way unique to postmodernism.