Offred
You insist that a society's moral beliefs has nothing to do with its laws. Where, then, do you think laws come from? Why do we in the UK have a different set of laws to e.g. Saudi Arabia?
What do you think of this:
"To the chagrin of some (Holmes, 1897), law trades in morals. At a minimum, the law prescribes and proscribes morally laden behaviors, but it also unabashedly attempts to shape moral attitudes and beliefs. When the law forbids murder, we know that this is because the law has decided that murder is evil, and wishes all citizens to agree with that assessment. When the law demands ‘‘good Samaritanism’’ in certain circumstances, we understand it to reflect a judgment that failing to aid those in distress is not just (perhaps) wasteful or inefficient, but is morally wrong.
The ambition of anti-discrimination laws is not just to change the behaviors of employers, landlords, and school administrators, but to change both cognitions about and emotions toward stereotyped groups (Allport, 1954). Sometimes, the law engages in moral regulation even where it cannot plausibly be aiming to change behaviors, attitudes, or emotions; the law simply expresses moral commitments shared (often very controversially) by the polity at large. "
Bilz, K. and Nadler, J. (2009) "Law, Psychology, and Morality", Psychology of Learning and Motivation, vol. 50
I think laws both shape and are shaped by current moral values. A society's morals change over time as can an individual's.
As for the topic of the thread, it's good to question traditional beliefs. It doesn't mean we want to show they're wrong, just to check that they are right and to understand them, maybe.
I think cheating is immoral because it's harmful to others and it's dishonest. Whether a particular case of adultery is cheating or not, or how bad a case of cheating it is, depends on the individual circumstances.
Therefore adultery should not be a criminal offence. Where adultery is/was a criminal offence I think it is due to religious and sexist/misogynist influences rather than any concern about harm done to the people involved.