I'll be honest with you: I think that it's really difficult, this framing around 'good cops' and 'bad cops.' Policing, as a system, is incredibly corrupt, period.
I've had negative experiences with cops. I've had positive experiences with cops.
Cops and robbers resemble each other, so there's not a lot to learn in terms of learning the logistics of committing the crime or investigating the crime.
I live in New York City, and one day many years ago I was with a poet, Gregory Corso, walking through Greenwich Village. He pointed to a doorway in an alley that he said led to a tunnel under Manhattan, a tunnel he'd use to run from the cops. I started learning about old Prohibition-era speakeasy tunnels under the city, for running whiskey.
The only thing police patrol cops - in certain situations - are expert at is spotting anomalies. When you are a black person that is driving in a place that you stick out, that's all they're going to see.
When you're writing about cops from the perspective of cops, that level of sarcasm about their job and how they treat people will color the writing to a certain extent.
It is a different genre - a show about something other than doctors, lawyers and cops. Teachers are something completely different. I think it makes for very interesting television.