It's easy, imagine your friend is being arrested by speed over-limit. It's what the police has to do, isn't? The thing is, imagine, that you record it, and then show the face of the police to your friends and you go to fight him. It's well known that sometime police should be recorded, but don't forget there is people out there which is hateful. Police, in general also need security. It's by that, so hard to find the best rule for all the cases.