I do think that the majority of police are decent people who care about the population as a whole and are working to further justice and well-being.

The problem is that not all police officers are like that, and you can't tell the good ones from the bad ones by looking at them. That means that we have to trust the police as a whole to ensure that the bad ones are removed from the police force.

The police generally have not been very good about getting rid of the bad cops. In fact, there's a tendency for cops to defend them for cultural reasons. Unless police culture begins to be even less accepting of police misconduct than the general public, all police have to be treated with caution.