Its an economic issue. If you are in an impoverished area, the best you can hope for is a few hundred a paycheck, which more often than not, covers just bills and nothing else, so say something happens, your car breaks down, you need $700 to fix it, which pretty much exceeds your monthly income, let alone your handful of free dollars. If you dont fix it you cant get to work, you lose your job, you lose your home. thats a desperate situation, desperate enough to where selling drugs becomes an option.

Now you are not the only person in this situation and other people are doing the same, so they are your competition, you need to either beat them, or join them. you cant join them all, you cant beat them all, so you gang up and fend off the rival gangs to ensure your income.

On top of this, the police are targeting all of you, and when you are caught, you are locked in a cage, and you are immediately facing between $600-$10,000 in legal fees. Now remember, you were only doing this because you were broke and desperate to begin with, and now you are even more broke, and even more desperate, and the only option you have to come up with that kind of money is to step your serving game up and move some weight, and that makes you a target, so now you have to carry big bangers to keep them boys from jackin your shit. Or maybe you need to come up and you know some boys that jacked your shit from before that you know have weight on hand, so robbing those fools becomes an option. This is the "black on black violence" you speak of. Its desperate people drowning, and there is only so much floating debris that they can latch onto to stay afloat. Someone has to get dunked under in order for you to survive because you dont want to drown.

The police are not directly responsible, but they are greatly exacerbating the situation. Getting them out, making them stand down, gives some breathing room to get the shit under control.