Of course there are bad police officers out there. There are some are dumb, some lazy, some corrupt, some criminals with a badge, some flat out killers, and some racist cops on the street. Nobody with a brain would deny this.
There is an estimated 1000-1400 arrest related killings a year in the US. There are an estimated 765,000 law enforcement officers in the US. There is an estimated 12 Million-15 million arrest per year made. So there is a arrest related killing in .0001of the total arrests made. That is basically 1 in every 8,600-10,600 arrests.
The Washington post is tracking the number for the current year and you can check it an any time.
https://www.washingtonpost.com/graphics/national/police-shootings-2017/
It says right on the page a quarter of these shootings are related to mental illness.
I know a guy who used to be a cop in a small po dunk Iowa town. He quit when a guy on meth pulled a knife on him. I never asked the details, as he really didn't want to talk about it, but I know nobody died. He just said that it isn't worth it to be a cop. My wife's family knew the female cop who was shot in the face by a meth head in Sioux City about 1-2 years ago. She lived, she was shot 1-2 months before her wedding. She had been to this person's residence several times on calls, this time the guy shot her in the face. Those of us in Des Moines all know about the 2 cops who were gunned down by the guy in Urbandale not that long ago.
This post isn't meant to excuse criminal behavior by the cops when they do engage in criminal behavior. We just have to be able to have a reasonable discussion about this topic. The cops do a very dangerous job, we have to understand that. At the same time, we can't just let them do whatever and get away with murder if that is what they did to someone.