Please see my post # 29.
A law is either mandatory, or it is not.
It does not make much sense to pass a law that is not mandatory.
This practice of passing optional laws is a very bad one.
There is often substantial value in having a respected entity--government or otherwise--openly proclaim various expected standards of behavior, even if the only only "punishment" for non-compliance is that one's behavior will be regarded as being outside the norm. Consider, for example, the laws which specify the correct orientation for a U.S. flag which is hanging over a a road. If someone wanted to hang their flag over a road in a fashion contrary to the law, the person wouldn't be subject to arrest or fined, but anyone who saw the flag would know that it was backward.
Basically, the law in this case is a statement of what people should do, and what they should expect others to do. In many cases, social pressures are in fact more effective than government punishments in promoting compliance with societal norms.