Yes, the rap genre is full of nothing but negative things about the authorities and a lot of other important things. I think that we need to put some censors on the types of language that they are allowed to use in their songs since a lot of kids listen to them.
I believe the 1996 shooting death of Tupac Shakur had far more to do with it than just that of the music industry. The same can be said for Notorious B.I.G.'s death. Rap does include vulgarity, crudeness, and a lack of respect and this has been common in the medium. It however, is not the only reason you see violence between members of the genre in the 1990's. There was a gang war going on that was quite involved and much larger then both of the rappers it killed.
Rap has evolved into a very aggressive type of music, but not to the extent that it would evoke listeners to go out and murder. Most rap songs highlight women and money, a divergence from 80s rap that promoted a "thug life". Also, I don't believe that rap causes listeners to commit crimes, but those who listen to rap are more likely to commit crimes in the first place. A Socioeconomic view suggests that rap is most popular among poverty, where crime is already a factor, rap or not.
There are many controversial songs in rap. Also, there are many controversial songs throughout all genres and throughout history, and the furore around rap is just the latest in a tradition of the older generations fearing newer pop culture - especially when they see it as eroding traditional values and society.
Rap music itself does not cause murders or deaths. It does not cause violence. It's a form of music that comes from a street culture that is already violent. Rao is a reflection of it is surroundings. Gangster rappers get shot because they are gangsters, not rappers. While the music might glorify the thug life, it is not the cause of it.
This question can come up a lot. Some rappers address the issue. One example is 'Like Toy Soldiers' by Eminem. He tries to show how feuds get out of hand. Rap can be used as an easy target because the artists vent their anger in a few of the songs. If those songs get popular, it gets to be a problem. Most songs do not involve the things mentioned in the question.