Why do members of the public know more about the law than the police?

Everyone should be very concerned that members of the public know more about the law than the police.
Why are the police not being taught about the law and what they can and can't do.
How embarrassing for the constables that they have to be educated by a man with a camera.
What a complete waste of police time when it takes five constables and a sergeant just for a man with a camera.