I actually wrote a paper for school about the influences of rap music and its effect on the communities from which the rappers themselves come from. I also just bought a book (I'm not too far into it yet) called "The Hip Hop Wars" where it talks about the media's attack on hip hop culture.
The problem is that much of mainstream media does not understand rap or where the lyrics are coming from. Some may sound violent, but I specifically cited in my paper a song from the newest Mobb Deep album (I know, it's G-Unit Mobb Deep and not the real Mobb but it still has a lot of relevance), in which Prodigy I believe claims he feels left deserted by God in the hood and his projects. He says he will beat God down if he doesn't get into heaven because he was given no signs he was being watched over by Him and felt left alone. The issue is that white mainstream media (see: Bill O'Reilly) will claim this shows a violent nature. My paper basically was about not that the violent rap lyrics created violent and destitute neighborhoods, but rather that the violent and destitute neigborhoods create the violent lyrics. What white mainstream media fails to understand is a lot of the violence set forth in rap lyrics is a reflection of the neighborhoods in which people grew up. I cited Russel Simmons who criticized the government's war on rap stating that the government should, rather than attack the people talking about violence, attack the source of why the rappers see violence and destitution in their neighborhoods.
I agree with a lot of the sentiment on this board, that the south especially has watered down rap but it's actually a lot deeper than that. There is still rap out there that purports reflections on society. The problem is that white record executives want to sell an oversexualized black male and female image, that reflects partying and drinking and sexual promiscuity because it is a caricature of the black man. The white man holds the key to record sales, as most record execs are white (even if black people own the label, distributors are primarily white). Rather than sign people who have disdain for the the system and would look to revolutionize black people's roles in society (and thus limit white people's power over society), they will sign people they think will sell record, promote "club songs" and videos that keep the black rapper in a subservient position. I don't know if any body has heard Skills' 2008 Rap Up, but in it he makes a statement about the rap scene in general, making fun of T-Pain:
And y'all in his lane
with songs like "OHHH We Pop Champagne"
So Imma say this quick: We in a recession
Y'all ain't poppin ****
If you haven't heard the Skills Rap Up get on that ****, it's hot and he's actually got a good message like "It's a time for a change/so don't go turnin inaguration into an all-star game/let's act right/and show these kids/we can turn yes we can into yes we did".
There's is rap with a message out there, but don't expect to hear it on the radio.