There are maybe two ways in which hip-hop sets itself apart from the criminally minded pop music of the past: by being so explicit about it and by being so black.
On the first count it's only guilty by a matter of degrees. Tune in to a classic-rock station for an afternoon and you're virtually guaranteed at least one song from the late 70s detailing the dangerous luxury of the cocaine smuggler's lifestyle. (Though as far as I'm aware, no one's ever tried to hold Steve Miller or Don Henley responsible for violence in Colombia or the lives ruined by coke addiction.)
As for the second, hip-hop was born just before the crack epidemic began, and the shape it took was molded for better and for worse by an environment of violence that for years was conspicuously ignored by nonblack America. For the most part, it continues to be ignored. The major exceptions are cases like Coleman's murder, where there's an apparent easy solution—"rap music did it"—to a problem that's the end result of a bewildering number of factors stretching as far back as the racial attitudes of midcentury city planners and beyond. The crack era has produced a fascinatingly broad range of artistic expressions, among them positivity in the face of overwhelmingly negative odds and, yes, the brutally ignorant stuff Chief Keef and Lil JoJo have made, which just so happens to fit the fevered image of the black thug that afflicts more nonblack Americans than are willing to admit it.
Rap music didn't kill Joseph Coleman. Music, like all art, has the power to affect lives, but it's more a reflection of its environment than a steering factor in it. If millions of young listeners were so impressionable that they'd mold their entire lives to fit what a rapper says, it would stand to reason that Jay-Z—one of the most popular hip-hop musicians of all time, who espouses a message of triumph over adverse circumstances via capitalism—would have solved the problem of inner-city crime when he dropped "Izzo (H.O.V.A.)," a monster hit in which he explicitly encourages young people to pursue legitimate entrepreneurship rather than the drug trade.
The only thing rap music contributed to Joseph Coleman's murder is a contextual framework that allowed his beef with Chief Keef, Lil Reese, and the GBE crew to escalate, in visibility and probably in severity. With higher profiles to protect, things such as the video Coleman's brother CashOut made, where he flashes gang signs and apparently has a phone conversation with Keef's mother about their supposed sexual relationship, probably mattered more. The stakes were higher.
But the problem here isn't the amount of crime and violence in the music JoJo, Keef, and the rest of those involved have made. It's the fact that for whatever reason the city of Chicago—its government and its people—have abandoned the south side to a plague of violence that's become so inescapable that it's practically the only subject the musicians from those neighborhoods have to talk about.
This isn't rap beef. This is gang beef in a rap setting. If you want to see something really depressing, you can trawl around social networks and find the same kinds of shockingly cold-blooded videos and tweets going back and forth between gangbangers who don't have burgeoning rap careers or anything else that would cause anyone from outside the neighborhood to care—the kind of young people who turn into nameless weekend-fatality statistics. They don't even get any music out of it.