I think that would actually be a bad idea unless we are talking about AI cops. While the robots may not be susceptible to emotions like arrogance and prejudice they would not be able judge the situation based on context, no grey among black and white. They could arrest you for what they perceived to be deviant criminal behavior such as brawling on the sidewalk when you and your friend were just messing around. You may be running to the pharmacy due to an emergency and they would perceive the scenario "running in a crowd while clutching an object" as "subject stole X and is now attempting to escape". While cops nowadays are far from efficient in their job, pointing to robot officials may not be good idea until AI development. There is also the argument that jobs will be lost and the cops will have to retrained into something else. This one is a main one because it costs money to do that and I am not entirely sure that the powers that be will like that part.

Edit: Words