The problem that those entrusted with responsibility will fail to exercise the diligence they're paid to exercise, but will instead act in their own interest to do things that are more convenient to themselves personally, is so well-known that the management literature has developed a term of art to describe it: the agency problem. The agency problem confronts voters whose legislators enact undesirable laws at the behest of monied special interests just as it confronts citizens whose police decide to use their badges and guns for some purpose other than to protect and serve.
Or … choose simply to protect and serve only their buddies with badges and guns. In one case, a Missouri police officer who answered honest questions about the in-custody death of a college student (accused of a misdemeanor) was effectively punished by his superiors for stepping out of line. Allowing police to be held accountable to the public isn't in the interest of the self-interested police. Read about the case here.
The problem isn't police only. The problem is the agency problem and its solutions are applicable to shareholders who want Boards who protect shareholders instead of looting the firm to enrich themselves, to protect voters who want legislators to pass laws that comport with public concepts of justice and reason, and to protect members of the public who don't want to fear violence from police who are protected from the consequence of any misconduct they choose to commit. The agency problem is the problem of business just as it is the problem of democracy.
Faithful agents mean the difference between justice and oppression, fair returns and fraud losses, free elections and a mislead public.
The agency problem matters.