People should read the original essay where they came up with the term. The so-called PMC is really just them trying to sneak in a white collar-blue collar divide while dressing it up with faux Marxist language. For example, they basically consider nurses to be part of the PMC because nurses are professionals who work in healthcare. Not sure what nurses have in common with software engineers outside of being workers. Nursing as a profession isn't even pampered at all, so the white collar-blue collar cultural divide of white collar being pampered doesn't apply to nursing.
In general, most service jobs don't fit well into the white collar-blue collar divide, which leads to patsocs labeling baristas as PMC. At this point, PMC just means "not blue collar," so a lot of neither-white-collar-nor-blue-collar occupations like baristas, sex workers, nursing, waiters, and flight attendants gets lumped in with lawyers, doctors, and engineers. Baristas, sex workers, nursing, waiters, and flight attendants are basically a different colored collar from white collar or blue collar, which reinforces the point that dividing the working class over their perceived colored collar work is ridiculous.