> They have been getting positive reinforcement by being not prosecuted and being protected by their force and the system in general.
Also, a number of cases have come out recently of police were disciplined, including dismissals, for reporting or intervening against excessive use of force by other cops, so there is negative reinforcement for good cops as well as positive reinforcement for the bad ones.
"Positive" and "negative" in reinforcement don't mean "good, pleasant, desired" and "bad, unpleasant, not desired". They mean "something was added" and "something was taken away". Better names would be "additive" and "subtractive".
The term for "good, pleasant, desired" is "reinforcement", for "bad, unpleasant, not desired" is punishment.
So:
Positive reinforcement --> Behaviour leads to addition of pleasurable stimulus. Eg. Press button, receive food.
Negative reinforcement --> Behaviour leads to removal of unpleasant stimulus. Eg. Press button, persistent loud noise is muted.
Positive punishment --> Behaviour leads to addition of unpleasant stimulus. Eg. Press button, loud noise begins.
Negative punishment --> Behaviour leads to removal of pleasant stimulus. Eg. Press button, food is taken away.
Also, a number of cases have come out recently of police were disciplined, including dismissals, for reporting or intervening against excessive use of force by other cops, so there is negative reinforcement for good cops as well as positive reinforcement for the bad ones.