That belief makes sense in a way, as all heavy-metal fans are white 
Although I would probably be perceived as a liberal by Americans I am against P.C.
P.C. is a form of censorship used by people that make assertations that they can’t back up by rational debate.
If someone says something that they don’t want to hear, or something that they’d like not to believe but can’t prove wrong using logic or scientific evidence; then they condemn the person guilty of disagreeing with them as being some sort of bigot.
They then use this as their excuse to run away from debate, a method of gagging their opponents if you will, by saying that any sensible debate is impossible.
In fact if factual correctness was in their corner of the ring then they would easily dismiss the P.C.“outlaws” suppposedly false premises ;and far from avoiding debate would actively welcome it.
When we see censorship in a Nazi or communist dictatorship we are expected to see it as yet another face of total evil(correctly I.M.O.) ,but when we see the same thing foisted on us in a liberal democracy we’re somehow supposed to look on it as a weapon of truth and light.
Of course P.C. is also used by people who wish to assert that they are “Holier then Thou”.
The sort of person that walks around looking for any excuse to castigate other people with assumed outrage for supposed contraventions of P.C…
The idea being that others will see how much more caring and saintly they are then the normal mass of humanity.
For which ever reason P.C. is foisted upon us its a very unhealthy practice.
To say that you shouldn’t call people with mental issues “fruitcakes” is not political correctness.
To say that, because some people use the term “fruitcakes” to describe people with mental issues we should avoid using the term “fruitcake” to describe a dense cake containing rum and candied fruit, is political correctness.