Police corruption can manifested in several forms. Whether it's unnecessary brute force upon making an arrest, or accepting bribes from organized and petty criminals alike, in exchange for amnesty and cooperation with these offenders.
Any example has one thing in common: each stems from a lack of respect for the safety and well-being of the public as a whole, and a failure to protect and serve the members of that collective entity.
Corruption and irresponsibility of such a powerful and universal organization is an extremely frightening prospect. After we lose order among those who work to maintain it, what security do we have as a society?