And yet THEY, the Cops, did not write the laws. Our elected representatives did. It is not they, it is us. The Cops do what we direct them to do. They do not run their cities, they are answerable to elected officials (as well as to the courts). If this activity, or any activity, is illegal it is because our elected representatives made it so. If those representatives made it so against our wishes we should have been more vigilant in watching them.
As far as I know, no police force is running an American city. They are not occupiers. They are not dictators. They are answerable to the people. Many problems arise, however, when a person comes to believe that they are "the people". Individual persons often believe they can tell the cops how to do their job, when, and where. They want to legislate and to litigate on the streets once an action has jumped off. The streets are no place for arguing ones rights with cops, we have courts for that. Cops do not work for any individual person, they work for "the people", society. If you want to argue with a cop, and there are certainly times when you should, do so in the courts, through elections, or through the legislature, not on the streets, and particularly not during a crisis you have precipitated. Crisis reaction is always uncertain