it's only a bad idea if the police have control over the recordings ... then you would see incriminating footage getting lost or deleted (and blamed on "equipment failure" ) & only exculpatory (for the police) footage being preserved.
I'm all for it (despite the expansion of the panopticon) if the cameras are always on (including an officer recall if the feed fails), the feed is streamed to a remote location, the record is administered by a public advocacy agency and available for public review, and all interactions of a routine nature are deleted after a fixed period of time.