So for them, winning the power game is the whole point. Saying nothing and changing the channel makes them the loser. Making you shut up makes them the winner (in their view).
Power? No.
Society enforces its rules. Get over it. And PC is about rules which generally enhance peace and cooperation. Being at the receiving end of a racial slur rarely puts someone in a peaceful and cooperative mood...
"Gonzales: There is one question, Inspector Callahan: Why do they call you "Dirty Harry"?
De Georgio: Ah that's one thing about our Harry, doesn't play any favorites! Harry hates everybody: Limeys, Micks, Hebes, Fat Dagos, Niggers, Honkies, Chinks, you name it.
Gonzales: How does he feel about Mexicans?
De Georgio: Ask him.
Harry Callahan: Especially Spics."
This wouldn't be funny without the taboo that was strengthening at the time.
No, today's PC has nothing to do with anything "peaceful and cooperative", not when it consigns to perdition all of us white heteronormatives in fly-over country, probably more than half the country. It has no limiting principle, is frankly totalitarian, and the end game is going to be arbitrarily ugly.
Just imagine the worst nickname anyone ever gave you, and having it replace your real name. That's about the level of rage people can feel about "nigger", "Injun", "raghead" or whatever you might imagine.
If you are transmitting over a channel where some amount of politeness is the standard, violating this standard will and should have consequences.
