You seem to see through the deception, but most don't. The whole policing house of cards is built on the idea that they "stop crime". They don't really, as you point out. In general, they do a pretty terrible job cleaning up after crimes occur, too.
The one thing that police consistently and effectively do is themselves act as a criminal organization outside the law. They cause destruction and mayhem regularly on very flimsy premises and see little to no oversight for it.