What Are Your Examples of Scarecrow Laws?

I'm working on a book chapter about filial support laws, where families (usually adult children) may be surprised to learn that their state or their country has a seldom-used law that mandates financial support or maintenance for indigent family members. In working on this chapter, I was considering using the concept of "scarecrow laws" as a metaphor.  This label can apply to laws which are seldom enforced but legislators resist repeal because the very existence of the law might serve as a warning -- a scarecrow -- about the consequences of bad behavior.

While working on the metaphor, I came across an interesting application from Shakespeare's play, Measure for Measure.  In Act 2, Scene 1, we hear a harshly ambitious deputy administrator calling for the ultimate punishment -- beheading -- of Claudio, a man convicted of a crime.  But the law in question, prohibiting sexual relations outside of sanctioned marriage, is "rarely enforced."  One of Angelo's subordinates objects to the harsh sentence. Angelo responds:

We must not make a scarecrow of the law,

Settling it up to fear the birds of prey,

And let it keep one shape, till custom make it 

Their perch and not their terror.

The irony is that Angelo also seeks to violate the same law with a woman who has attracted his attention, but he discounts his own admission as, so far, mere temptation.  

Shakespeare's use of the scarecrow characterization raises a legitimate question.  Should laws, little known and rarely enforced, be removed from the books, or allowed to remain, perhaps on the justification they serve as moral guidance?