Police are always in the middle. On one side is the citizen, who is having the worst day of their life courtesy of the person on the other side, the criminal. The criminal operates with no artificial restrictions on their actions. The idea of honor among criminals is a joke maintained by TV. A criminal is a citizen until they become a criminal, and then they remain a citizen until their action are proven beyond a shadow of a doubt in a court of law in front of 12 skeptical citizens who watch too much television.
The police are usually armed worse than criminal. A criminal knows that this is the day they will bring an AK47 to work. If we carry the big heat citizens get pissed. Nothing worse than an elementary school teaching bitching you out in front of your kids when you drop them off at school because your pistol holds four more rounds of ammunition than they think is cool. You have to stand there and take it because it is your job, saying yes ma'am.
(In an MMO it will be worse. With at most a 45 minute cool down for the most heinous crimes one criminal can commit ten violent acts a day (if they have no life) and no real reason not to go down shooting up the town square, the server in a few hours can become a wild west show with no business able to operate, no one able to walk the street, and everyone hiding in their apartments waiting for ceasefire that never happens.)
So how do we keep the peace and RP at the same time? By doing it like professionals and using radios and record keeping.
Patrol officers are the most vulnerable but most essential part of the police force. A patrol officer has a beat that they should walk - if you never get out of your car you miss a lot. The patrol officer is the trained eyes of the rest of the department. They meet with the citizens in their beat, solve minor issues before they become legal issues, and look for people who behavioral patterns indicate they could have issues that may affect the community. It is possible this will be an impossible job. In an MMO server with no real penalties, patrol cops will spend more time dead from ambush by any noob or ganker on the server, but if the patrol system breaks down, effective policing does.
(In real life the death of a patrol officer causes police departments to go bananas . Everyone started here, and everyone knows if the bad guys want you bad enough, they will get you and all of your training, experience, and practice will drain out into a gutter in seconds flat. )
At the same time the patrol officer cannot be corrupt. A corrupt patrol officer is part of the problem, not part of the solution. Most officers will look the other way for small offenses, but CDV, DUI, and any form of assault on up will get an officer forever banned from a modern police force. Corrupt police forces exist, but they are nothing more than another gang dressed in uniforms.
A police officer has those two advantages I mentioned before to aid them. Any officer who finds themselves in hot water can call on the radio and get a partner. That partner can call and get the squad. The corporal can call and get the district. The sergeants can ask the Lieutenant to request SWAT. When a gang member is in trouble, other gang members generally flee. There is no honor except on TV. When an officer is in trouble it is like a black hole sucking more and more officers to the aid until the bad guys are down and out. And if the bad guys kill me, my friends will never stop until the bad guy pays the full legal price.
Plus we have records. Bad guys have no institutional memory, and live in a subjective bubble of slights and misdemeanors. We have records. We do not have to guess if you are a bad actor, we can find out by looking at your file. You can walk down the street and buy a Pepsi and we will not look twice, but if you are holding a smoking gun and have record of shooting at people, we will have a record of it, and that record is often how we catch you. Juries are gullible. they want to believe the poor picked upon bank robber who was only getting change for a five with his shotgun when the heinous police barge in and made a big deal of it. But juries hate looking stupid. A guy who tried to get change for a five with a shotgun ten times will find that they run out of bargaining power.
So radios and record keeping are essential to being a police officer, and will be all that keeps us active if the server rapidly degenerates into sarajevo complete with sniper ally.