This does answer my question in a very satisfactory way.

Since you mention Ferguson, the theory I currently hold is that tensions between the police and the policed are, in practice, inevitable if the two differ in race, ethnicity, language or religion. Through their sheer visibility these differences have more weight than any difference that otherwise exists between the government and those it governs. The only plausible way to resolve this tension that I see is by ensuring the police force of a community is recruited from that community and represents its ethnic and cultural makeup.