People just don't realize that cops get fired all the time for things. Not terrible things either, minor things that most of us do daily and are allowed to do at our jobs. But we never see those because they aren't news worthy.
They also get disciplined all the time, once again, not for huge things, but for relatively minor things. But we never see it.
You just see the stink over the big things, and you see it because they are generally ambiguous. Nearly all of them involve a suspect presenting a threat. It may not be blatantly lethal, but they don't involve law abiding citizens going about their daily business in a peaceful and productive manner. This is why other cops generally don't act, or come out against it. Because they know they could be in that position one day to make that split second decision in an ambiguous situation.
Same thing with doctors.
Preventable medical mistakes kill upwards of 100,000 Americans each year.
But we rarely hear about those. Why? Because the vast majority of people recognize medicine as a difficult area where things can go wrong for even the best doctors. We recognize that it carries risks and that doctors are generally doing the best they can given the situations and information they have. Which is why we don't crucify and jail doctors very often, nearly never.
But police aren't given that luxury. And it is mainly because people get punished by the police. They break the law, they get caught, so they hate the police, which causes them to be unable to look at the situation objectively. And that is why we have the cop hate.