The basic rule always should be that you don't say things to hurt other people. There are some names which do hurt and insult other people, or that encourage bad attitudes towards them. Anyone half-way decent will try to avoid using names like that any time they can.

The trouble about making hard rules about this kind - what has been lumbered with the term PC is that it's too mechanical. It's like painting by numbers. If the attitudes behind the words stay the same, changing the words doesn't solve things. At best it can be a tool for trying to change some of those attitudes, but a pretty blunt tool.

That doesn't mean its not a good thing to get rid of words that have become insults. But words change and people change, and what's harmless today will be offensive tomorrow, and vice-versa. So long as there are people who want to insult other people, or see them as less than human, they are going to take whatever words there are, and use them in a way that conveys that. What happens is that the "new" words, the words that today would be called PC, become insults, because that is how they are used by people whose attitudes haven't changed.

And what also happens is that people who wish to promote division and hatred make up phony PC stories, or hunt out occasional absurdities, and spread them like urban legends.

And what also happens is that ambitious little tykes in positions of small authority have at times fed into that. They have seen PC as a toll they can use for office or academic politics and so forth, and these are the people who tend to lie behind the "occasional absurdities".

And sometimes they do it intentionally, because they want to promote division and hatred themselves. And I strongly suspect it was people like that who invented the absurd term PC in the first place. Hell, what is so "political" about being courteous to people who have been insulted every day of their lives?.