Law and Morality

The literal rule is usually quite clear and provides certainty as to precisely what is illegal.
It's very helpful when dealing with simple crimes that have strict or absolute liability- like speeding or polluting rivers.
Less useful for handling more complex crimes that focus very strongly on intent or involve technology and problematic social issues that are emotive or very widespread.

The problem tends to come when dealing with morality based archaic laws in modern scenarios that the original law was not designed to handle.
For example upskirting, a judge decided based on the literal rule that upskirting was not a crime if the victim was wearing underwear.
Although the creep was willing to plead guilty and the CPS were willing to accept the guilty plea- the judge used the literal rule about what the victim was wearing along with his own personal viewpoint to decide what was indecent and intended to be outlawed.
The focus was on the literal meaning of the statute words, combined with the choices of the victim rather than the actions and intentions of the defendant.

Other judges have used either golden or mischief to convict the pervert- to shift the legal focus onto the actions of the creep filming or photographing up a woman's skirt without her consent.

At the time the laws on public decency were created, opinions were very different than today and the everyday technology that we take for granted didn't exist.
Laws focused on morality based upon religious attitudes and the problems that were worst feared or widespread at that time.
Books with sexual content or controversial theories were considered dangerous and taboo.
Creeps trespassing on private land, sneaking into other people's gardens to peer at young women through bathroom or bedroom widows, were held to be the indecent bad men of the era.
The laws was intended to punish these scenarios and deterring potential wrongdoers from going down such a path.