Note that it is not a violation of anyone's privacy. Police interactions with the public cannot be private, with the only exception being undercover police work or other times when the identity of the other person must be protected as in the case of a minor. These cameras can and will prevent petty (and egregious) abuses of power that American police have grown used to getting away with. Right now there are insufficient safeguards against police misconduct, and ubiquitious cameras would be a good step toward making those safeguards sufficient.