You can say what you want to about a rapper in a movie, but look at what Ice Cube has done. Ice Cube has created more opportunities for other actors to get jobs in this business than some actors have.
Some of these guys... I've worked with Ice Cube, I think he's an immensely talented rapper and actor.
You take the quote from Sam Jackson about how he'll never work with a rapper, and I can understand where he's coming from because he says rappers can't act.