The lyrics of most rap music contains direct suggestions and rewards to the use of drugs and alcohol. A good example of a direct connection to drugs and alcohol is the lyrics in the song "Pass the Courvoisier" by rap artist Busta Rhymes. Another good example is the marketing and advertising used by rap groups to promote their products and concerts. A close look at the rap marketing objectives and one will find a direct connection between the use of drugs and alcohol and why one should listen to the music.
It's true some rappers glorify drugs and violence. They even try to live the life they rap about (like Shmurda). But more rappers are the exact opposite, and do not glorify drugs and violence. Some of the most popular rappers of the day, like Kendrick Lamar, actually have anti-drug and anti-violence messages. The 90s are gone. Most people do not want to hear violent rap like what was popular years ago. If anything, sexism is more prevalent.
I do not think rap and/or hip hop music hinges specifically on drugs and violence. To me, when it comes to rap music, drugs and violence are simply a part of the lyrics and nothing much else to it. People should not take what they hear in rap music so literally.
If this were the 90's, then this question might be more of a debate. But popular rap music today doesn't even mirror old school rap. Current popular rap is typically about what most pop songs are about these days: partying, money, and booties and apparently just about anyone can call themselves a rapper now. Sure, today's rap songs may mention drugs or violence, but so does pop music. While there are some exceptions, most rappers of today know nothing of hood life or the struggle, the very things that rap was born from.