I don't think it has much to do with how many police are around. I think the salt Lake City Police Department takes a different line on simple possesion than the Sandy City Police Department. Beyond that, there's something I call "selective law enforcement" which is my term for a society where there are simply too many laws to enforce and many of the laws don't actually protect people, they simply are an attempt to control people and create a better society (like anti-drug laws). In that situation police have to select if they want to enforce laws or not. The police officer does not have to be racist, at all.
Imagine a disenfranchised young black man driving down the street. He is pulled over for rolling through a stop sign and then informed that he has a bad tail light. The police officer asks him to exit his vehicle. Once out the officer asks if he has any weapons:
"Are you carrying any weapons, sir? Any guns, knives, grenades, rocket launchers, anything like that?"
"haha, no"
"Ok, well, for my own safety do you mind if I check?"
"Sure, go ahead."
"Okay, sir. If you wouldn't mind, please turn around and put your hands up to shoulder height."
The man complies.
During the search the police officerpats down the upper torso of the young man. Then when he reaches the waist he says,
"You don't have anything sharp in your pockets, do you? No needles or anything? I don't want to spend the rest of my day at teh hospital getting all the shots they make me get if I get stuck."
"No, sir."
The police oficer pulls all the contents out of the man's pockets. He finds a lighter with some black resin on the side of it.
"Sir, will you please put your hands behind your back?"
"What?"
"Please put your hands behind your back."
"Why?"
"I need you to cooperate, sir. Please put your hands behind your back. This is for my safety."
"What did I do?"
"Sir, I'm only going to ask you one more time. Place your hands behind your back."
"But..."
And the police officer takes him to the ground, wrestles with the young man a little, gets his knee on the back of the man's neck and eventually cuffs him. Once cuffed the police officer searches the vehicle. He finds a small bag of marijuana. He goes back to the young man sitting on the curb in hand-cuffs waves the bag in his face and tells him he is under arrest for possesion of a controlled substance.
"If you simply would have cooperated we could have avoided all this," he says to the man.
The young man, on his way home from work, excited to see his wife and young son, needing to cash his check so they can pay the water bill, is now the latest beneficiary of our war on drugs. Because he only possesed a small amount of marijuana he is released on probation. He has to attend weekly group meetings, take random drug tests that he pays for, must attend AA or some other addiction prevention program and must notify any potential employer that he has a drug related arrest on his record. He gets very tired of his group meetings and after 4 months of doing everything he's asked to do he stops going to his group meetings. He gets a call from his probation officer. He has to spend three nights in jail and will have even more stringent requirements going forward. He's now "in the system, " and it's unlikely that he'll ever be out of it again. He will always be held to a different standard. he will always have a **** ton of BS to deal with in his everyday life if he wants to keep his freedom. Once he gives up or slips he'll be incarcerated.
Modern day Jim Crow.