take it the other way round : there is no need to have law if people respects each other. If people don't then ... you create a law.
In Europe, the law is not seen like it is in the US, it's not ON/OFF in a certain way, i know it's hard to understand for US citizen but we are used to "self discipline" and what can be admitted by the surrounding and what cannot, even if you have the law on your side. At the end of the day you need to live and be accepted by your surrounding EVEN if you think you have the law with you.
Where I live, metal detection is prohibited (not the metal detection, but the finds with the usage of a metal detector are illigal...). I detect a lot without any problem, because I respect people sensibility and feelings. I have been cought numerous time by Police without any futher action.
It this case, Law is the tool to prevent mass metal detecting bothering everyone. If you bother no one, then the law is not applied!
PS: sorry for my english, it's not my everyday language