Unless they are in places like Seattle. Remember the wacko riots there a few years ago? But, generally speaking, you are correct.
The riots in Seattle were almost a textbook example of bad police work by those in charge. They hired a security advisory group beforehand who made all sorts of recommendations and then decided to disregard them all. They let things get out of hand because they honestly seemed to think that Seattle was such a peaceful and tolerant city that nothing would happen there, despite knowing that anarchists had arrived in town with the intent of tearing things up. Then when things were really getting rowdy, they got a call from their fellow democrat in the White House telling them they'd better have things under control when he arrived in town the next day, so they responded with an iron fist.
If they had just planned for unrest in the first place and arrested the troublemakers before things got out of control it all would have been uneventful.