Police are not supposed to be a net good. They are a classic solution to a game theoretic prisoner's dilemma. If there were no enforcement of laws by police, it would be in everyone's best interest to e.g. steal. Regardless of whether other people steal, you'd be better off doing it. So as a classic solution to the prisoners dilemma, you introduce a force that strictly decreases everyone's utility function. How can this be a good thing? Well, because it changes everyone's optimal strategy from stealing to not stealing, reaching a global optimum. Now you'll notice that this strategy only improves things if it actually changes people's behavior. If people continue stealing anyway at the same rates, then things have only gotten worse (unless you subscribe to punitive, rather than deterrent punishment). So the primary purpose of police is deterrence through the threat of negative reinforcement, not "helping people". Further, whenever police actually have to enforce laws, its a sign that something has gone wildly wrong. The deterrent didn't work, and things are worse off than if there were no police at all. Of course, in reality criminal behavior has a lot of motivators and it's not possible to change everyone's optimal strategy just by raising punishments, so you're going to have police enforcing laws. But there is no police department that is more successful than one where the police just sit around and do nothing.