I think it's the same sort of deal that other positions of power have. Anybody that wants to be one probably shouldn't be one. (i.e. politicians)
Granted, some police are there to help. Others are there for less noble reasons.
Maybe we should have mandatory service like jury duty for things like police and political positions.
"Aww dammit! I'm president this year!"
Actually...considering the average person you meet on the street, scratch that idea.