what PRECISELY qualifies him to decide who IS entitled to express an opinion, and who is NOT?

If expressing your opinion amounts to an unqualified rant against something you have absolutely no experience or understanding of, which you clearly don't in this instance, then I'd say said opinion was really best kept to yourself. It's a negative outpouring - perhaps even trolling in Mudcat parlance - indicative of broader levels of such bigoted intolerance in the so-called folk community. As for what qualifies me to say this, simply my belief in living and letting live & that it takes all sorts to make a world.

As someone for whom all music is folk music as I've never heard a horse sing a song, then by that definition alone, rap is folk. There's nothing new about rap and hip hop, with an established & evolving structural vocabulary going way back, as has been shown. It is as old, if not older, than Folkie Folk Music, which only begins in 1954, born from a theoretical construct based on an interpretation of certain corporeal precedents which may, or may not, have seem themselves in that way, or in any way at all. Like all folklore, it's only the folklorists who perceive it as such.

In terms of both the Spleen Process and the Horse Definition, then rap, along with all world human musics, bar none, is folk music because all music is folk music by default. However, whether or not these musics see themselves as folk music is another matter entirely. Personally I doubt they would out of dread association with what Folkie Folk Music has become as a result of its own somewhat precious definition (1954 or otherwise) thus informing the self-serving bigoted myth that is the very worst of what Folkie Folk Music has become in its self-imposed cultural exile from folk music as a whole. You want evidence of that, look no further than this thread.