Thats a horrible argument. You have nothing to hide when you're taking a shit, everyone does it, but that doesn't mean you want it being recorded.
I agree on principal though. Police should be recorded, as often as possible. They are here to serve and protect, not to "clean up the streets" based on their personal or collective morals.
Not all cops are bad, I've, thankfully, have yet to encounter a "bad" cop. However, I believe that the common person needs more protection against police abuse of power, since it seems to be becoming more and more common.