In theory, J is correct about music being universal- it's why we can listen to music with foreign lyrics and be just as moved as we are when the music is in the same language as our own.
The problem comes in with the commercial aspect of music and I don't think that point is made very well when people talk about musical appropriation. You see, if we have a famous white singer doing music that is usually done in black American communities and that white singer keeps getting cash and awards while the black singers are left in the dust then it becomes a problem. We see this quite often.
Some sort of a problem comes in when we try to decide where music fits in terms of race because what we now consider black music might not have always been black music or what we consider, say, Irish music may well have been influenced centuries ago by another group of people. Musical history is complicated, to say the least, so it can be difficult to take complete claim to any sort of music. However, the problem I mentioned in the second paragraph is where the issues come in. Appropriation would be less of a problem, or perhaps no problem, if the music didn't get more attention only when white people do it. Unfortunately, that is the case now, but it's slowly changing.