Here's my point with the above comment that cops are responsible to stop dangerous behavior even if it's not illegal. I have a 5 year old that I take to playgrounds frequently. So let's say some teenagers show up with skateboards and are doing stunts on the playground equipment. And lets say, like most cities, that there is no law against that. But if a police officer is present and sees that there are children playing and the skateboarders are close enough to them that a botched stunt could cause a child to be injured, the policeman's duty is to tell the kids to stop. It's nothing against skateboarders or their rights to use public property, rather it's about the safety of everyone involved. If the cop perceived the drone pilot as posing a threat to the safety of others, right or wrong, it's his duty to speak up and stop the unsafe activity.