Szasz entire screed appears to be based on mental illnesses not being able to be concretely diagnosed or detected, but then jumping to the conclusion that they are completely made up and abused by society to control everyone's behavior.

Once you "accept" his conclusion, it doesn't seem possible to be argued out of it until science advances to an arbitrary point where one feels it adequately explains mental illnesses. "accept" in quotations as I honestly can't tell if his supporters are trolling or honestly believe what they're posting.