Why? What do you hope to achieve other than to possibly inflame the situation? I can't possibly believe that you think the cop is going to think "gee, that's a good point citizen, please carry on".
It forces the cop to either admit that he's a bad guy (or at least crossing the line), or else to not cross the line. It makes it so he can't try to pretend to me that he's squeaky clean while actually doing dirty stuff.
I don't think you're modeling the cop very well. They're not going to be in a state to reason or debate with you, and the statement "for your protection" if not paid close attention to sounds vaguely like a threat.