I was a late convert to rap. I don't like all of it by any means. But to dismiss it categorically is pretty ignorant, as ignorant as dismissing any entire genre of anything. By delving into rap I feel like I understand African-Americans and their culture a lot better - not by getting all of my info from hiphop music, but by absorbing what it has to say and cross-referencing it with other input from black activists, philosophers, other black-dominated music genres, even comedians.
For example I immersed myself in a sort of primer of gangsta/ghetto rap, consisting of the following albums:
Notorious B.I.G. - Ready to Die, Life After Death
Nas - Illmatic
Jay-Z - Reasonable Doubt
Dr. Dre - The Chronic
Jeru the Damaja - Sun Rises in the East
Even just this small segment, when I gave them all five listens apiece, caused me to absorb by osmosis a lot of information and attitude about racism, poverty, history, hopelessness vs. striving for betterment, and yes, a great deal of posturing, slang and preferred product references.
This is coming from an open-minded metalhead whose preferences formerly ranged from Slayer to Satriani, Metallica to Ministry, Carcass to Melvins, Tool to Minor Threat.