Robbing artistic producers, which is what the majority of rap purveyors are doing, by sampling (stealing) from other artists, mainly rock.
RAP is not music, and is very difficult to be considered music by any stretch of the word,
RAP is actually Rhythym and poetry... piss poor poetry, which was at one time very unique, until the second or third RAP spitter became popular, then it went south, because everything done since that very first one, has the same lyrics, just shifted around to a different computer beat.
RAP is popular because too many white juveniles want to fit in by appearing to be a "gangsta" or a "playa" because they listen to it.
RAP is popular with young blacks because it talks about the only things that many of them truly understand: poor speech, lack of formal education, lack of respect for themselves and anyone who doesn't look act and talk like them.
RAP exemplifies the "herd instinct" to look, talk, think and dress alike, just like the military, or the police, like one big "Gang mentality"... ie; no sense of individuality, which, of course means that RAP lovers need leadership, like sheep, and other bovines, thus, they follow the "lead" of the uneducated, unintelligent "wish they could be" musicians/poets.
RAP and it's popularity is proof of the sorry state of America, now that the uneducated, morally void have set a trend that has gained a massive following of ignorant youth.
The onset of this trend was the mid-1970's, when corporal punishment was outlawed in the public school system.