The way of semantics. PC is actually the opposite of being polite....it's being intolerant. Polite would be in respectfully disagreeing, not using rhetoric to attempt to inhibit, if not prevent, a differing thought or perspective.
It's consistent with how the pro-transgender crowd is attempting to redefine the Bill of Rights, when it refers to discrimination based on race or sex is unconstitutional. Sex here is clearly in relation to biology. ..not how someone feels, at any given time