It's not just talking, that's the thing.
Pitch still maters (if you don't beleive me, go see POD live and tell me the singer isn't flat and it doesn't help ruin the positive aspects of the band). Second, it has to be in rythm with the music, ie in meter. If rap is crap, so's Shakespear.

The way I see it, if somebody can get up and do it live, then I have no problem with what they are doing (well, unless it's plagurized or something). I have a lot respect for some rappers- Deep down I really see this as an issue of "music is art, and who's to say what's art or not?" sort of thing.

Do any of us really have the right to say that? That somebody's work isn't art just because we don't like it?