Political Correctness is despotism.
It is the establishment of the liberal agenda as the new social order. History and science are revised to support their positions.
It tolerates no dissent or questioning of the "facts". Liberal intellectuals have already decided these "truths". If you question them then you risk being labeled a "heretic", a sexist, a racist, etc...
"Diversity training" is re-education brainwashing, plain and simple. There is no tolerance for diversity of "conservative" views. If your support a different economic policy, it is because you are "greedy", "selfish", and "mean" (and maybe a "cheater" or "oppressor").
Political correctness is about brainwashing; getting that little censor in your own mind to "replace" words like mailman, lest you might offend someone. Why wait until someone voices a complaint? Avoid confrontations by censoring yourself. No one will see this. No one will note how many times such censoring occur. NOW there is a good backlash against such mind control. Initially it was just done with "good natured" ribbing and parodies (but people still went along with it). Now that we have seen news agencies refuse to call the 9-11 hijackers "terrorists", we know that we censor our language at our own peril.