For one, I am white. It is a rational expectation for me to hold that the police can be trusted... for me. One of the most crucial problems with any dialog in this country is that people assume that, because they see the police as a positive force, other people must similarly do so. Different experiences produce different outcomes.
However, I still do firmly believe that most police are decent people. I have heard police say that 10% of cops are heroic servants of the community, 10% are scum, and 80% go either way depending on who they're with. The point is to try to increase the size and influence of the first group, reduce the size and influence of the second group, and immunize the third group from the second. That requires substantial changing in policing tactics, socialization of police on the job, organizational culture, training, better diversity work, promoting more female officers, etc., but it can be done.