Imperial evidence? Empirical. And no, there haven't been any controlled experiments demonstrating my contention.

Rap and Hip Hop gave voice to a generation of African Americans who continue to be marginalized in America. It told America what was happening in the inner cities and brought questions of race, violence, and oppression into the mainstream debate. Look at Public Enemy and N.W.A. for examples. Not only that, it's proved to be a durable and flexible art form that's given rise to a ton of innovative and progressive artists.

I don't have to defend hip hop as an art form. It's obvious to anyone who's been paying attention that it's worthwhile, creative, varied, and important.