This reverses the subject, though: even if we grant that private civilians should have a (possibly limited) expectation of privacy in public, civilians acting in a public capacity, like the police, should not. Given the enormous power they have to act outside the law with impunity, removing the only check on that power— transparency into their conduct— would be a mistake. One only need to consider any of the many times police have been caught outright lying by video surfacing afterward to understand why.