Hip-hop has made an entire industry out of pulp violence. Some of the most affecting hip-hop makes you feel the consequences; most is unapologetic in its brash embrace of recklessness. Some of the most effective gangster rap is that which convinces you of its realism, and ultimately, puts you into the action. It's all about that vicarious thrill.
Some of the most harrowing music manages to convey the repercussions of squeezing triggers. The worst of the form is that which renders the violence banal, like an action movie or video game, while purporting the entire time to represent reality or hiding behind the myth of street reportage. Even the hip-hop that shuns violence is often shaped by it in the inverse.
Ironically, as time goes on and artists gain respectability, the violent subtext of their music becomes detached. (Think about how Jay-Z made his name in the early years, conveying a drug dealer's drama with threatening nonchalance, and contrast it with pictures of him with President Obama.) Calling a record a "classic" gives it a sheen of respectability that makes it difficult to remember what was so shocking about it in the first place.
In order to keep pushing forward, the cutting edge of the genre is continually reinventing how to make violence feel more and more real, to capture intangible feelings of tension and danger and give them some release.
As Ann Powers argued in her seminal piece In Defense of Nasty Art, "violator art begins with the premise that...negative feelings belong to us all, and we can't be cured of them." This is the rush that successful violent hip-hop seeks to replicate. Powers' mid '90s essay was inspired by Tha Dogg Pound, but the same case could be made for Kendrick Lamar. When it works, this sort of music feels visceral, true, and important, while the records that fail seem rote and extraordinarily exploitative.