If in this day and age you still think the police are here to protect and serve, you're either naive, indoctrinated or mentally handicapped.
Their primary role, first and foremost, is to act as revenue generators for the state. This is obvious based on the amount of victimless crime laws they enforce, all of which result in less money in the offender's pockets. Every now and then they'll do something of actual value, but this is greatly overshadowed by the parasitic nature inherent in most of their actions.
Like nearly all monopolies, a monopoly on security produces negative consequences. With no natural market forces at play such as competition, they don't need to worry much about customer satisfaction, public perception, service, etc..
And now a quote from the great Dr. Higgs:
