Photo radars are a reactive measure. If the goal is safety, and also eliminating carelessness and inattentiveness which we've ALL done, governors make the best sense as a proactive safety measure to save lives.
As far as cops, you have it backwards: Th static limits on any given road by our infallible authoritative experts following "The Science" in government have decided is SAFE, of all people involved, those in public SAFETY, who ENFORCE these perfect limits, should have these devices before anyone else does because they are sworn to uphold the law. For good reason, police chases are becoming less rare because its much harder to hide. The more we leave it up to machines to set the boundaries than a Barnie Fife with an attitude selectively enforcing the law, I'm actually for speed governors.
Manual driving is going to become very expensive soon because of the liability involved. I'd gladly give up driving if fleets of cars were autonomous. It allows much higher safer top speeds.