Rap was important and had a clear goal; to inspire afroamerican people, kids to learn, to live their life and fight for their rights. to get up from the ghetto, to keep on going, make them see they aren't alone, they have their backs by the community. (In the US)
this all was rather successfull.
but then, I don't know what rap's function is today. if there is any... so what you are saying, I can aggree with it, but I tend not to forget what was the original goal of this genre, and this is why I can't completely dismiss rap.