Yet again, we seem to be confusing things with ideas. While people do become emotionally attached to ideas -- and so can feel genuinely hurt -- when Person B else takes up** an idea from Person A, the original stays with Person A, whatever Person B does with that idea.
Oddly enough, the transmission of ideas is usually considered to be a good thing. We call it education. Countries, when they can afford to do so, pay to have their children -- and adults -- educated. It is seen as a Good Thing. And it is. The idea that we should teach people about how others live is also seen as a good thing. To say, at the end of such teaching, "Hands Off! It's not for you!" is essentially daft and, in a way, quite cruel.
It's only seen not to be daft through the lens of Privilege, where some people's cultures -- the culture of people who are privileged -- can be shared*** because, well, they're Privileged, but others' culture is protected, is placed in some sort of reservation.
The most worrying aspect of this whole thing is that it seems to emanate most strongly from educational institutions, particularly higher education, places where people should be being helped to learn how to learn and not, one would hope, to learn how to see the world as some sort of cultural museum, with the exhibits careful kept behind impenetrable barriers, to be seen but not to be experienced****.
** - As someone mentioned above, we do allow certain restrictions (patents, copyright) -- time limited restrictions -- with regard to new ideas thought up by one person (or a group of persons) so that they get a chance to benefit from them having that good idea. But eventually that protection runs out. (The enormous amount of time that this persists after the death of the owner of a copyright is ridiculous... except, perhaps, when the copyright owner dies young leaving dependents with nothing but that copyright.)
*** - Japanese musicians can, quite happily, listen to, play and write "western" classical music and people (quite rightly, in my view) see this as a good thing, not cultural appropriation. Now Japan is a democracy and one of the richest countries on the planet; a lot of "western" music classical music comes from relatively poor countries in Central and Eastern Europe which were, when Japan was taking up their music, more or less totalitarian states. In what way were they Privileged compared to the Japanese? They weren't. (Note: I know Japanese people were seen, by at least one horribly racist country, as "honorary whites", but I hope no-one here would think that this is a good reason to say that no "cultural appropriation" could be happening in this example; a better one is to dismiss "cultural appropriation" as the wrong solution to the problem of bad representations of The Other, whoever The Other happens to be.)
**** - I think the "experienced" bit is important. People who say, for example, "Watching a sport is simply not as good as participating in it," are correct. Living life as a series of vicarious experiences (other than those one is allowed to participate in) is no life at all. And where there are rules about allowing -- and, more particularly, not allowing -- certain experiences, they are going to result in: 1) a lot of people not even bothering to look, but stick to living with the things they're allowed to, diminishing their chances of empathising with people different to themselves; 2) a lot of people deciding that just because someone says that they can't do something, it's a very good reason to do it (which is perhaps not the best way to experience the culture of other people, people who've been taught to believe that this culture is theirs and theirs alone).