Yes. If a person has a certain lack of intelligence, simple opinions like musical preference can easily fester into closedmindedness, then rudeness, and eventually intolerance. Rap is just the new thing. People who like it will eventually start hanging out with other people who like it, and they are brought under the illusion that only "cool" people like it, because their friends like it, and they think their friends are "cool."
This also means that the "cool" people think the people who made the stuff that is "cool" are "cool," and want to emulate them. The only examples they have are through their material. Normally, this might just be playing music or having long hair or something, but the most popular form of rap, gangster rap, contains gang violence, prostitution, rampant drug-use, and excessive profanity. Other genres may have been played by drug-users, but few actually referenced it directly or as often as rap. I'm not saying it's the only "big thing" that was detrimental, I'm just saying it's the one that perpetuates the worst sort of activities. I'm not saying rap is going to make every little kid actually go out and do drive-by or something, but it probably will influence them to do whatever they can get away with, or act like they might do some gang-related violence, or act like they are in a gang.
My argument could also be used against video games. Most video games, however, feature obviously fictitious settings or stories, so doing the things in the games is nigh impossible. I'm sure a lot of kids who played Halo think it would be awesome to be a pwnsome SPARTAN fighting aliens. Most video games also only feature over-the-top activities. The whole "gangster" genre of anything, though, features things that would be easy to do. Do drugs, cuss, act like you're in a gang, etc.
So, yes, I think rap is relatively detrimental to society, because it popularizes illegal activities.
EDIT: I'm not saying all rap is bad, I'm just saying that gangster rap is bad. Not the music, but the people who make it, and what they popularize by putting it into the music. If you like the music, that's totally fine, just don't be an idiot. If this were about gangsters putting gang activities into rock music, that form of rock music would be detrimental. I might be a bit rambley here, but you guys get what I'm saying, right?