There are many cases were people are jailed arbitrarily, or unfairly. At no point in a legal case is the jury asked to consider whether it is moral to jail the defendant, only whether the law says they should be in jail. At best, the only moral leeway the legal system has is in the judge’s ability to change the magnitude of a sentence (which in many countries is severely hampered by mandatory minimums).
An individual’s morality may occasionally line up with law (especially if one’s subjective axiom is ‘Don’t break the law’), but this alignment is rarely if ever on purpose, but rather a coincidence.
As to who likes being in jail? Many a person has purposely committed crimes and handed themselves into the police because they prefer being in jail to being homeless, or prefer the lifestyle of living and surviving in jail to having to engage in the rat race, and so on.
Their utility function, rates the reduction in utility from the lack of freedom of jail less than the gain in utility from avoiding the rat race, or living on the street, etc.
Their morality can be objectively analyzed through science by simulating their utility function and objectively determining which actions will likely lead to high expectation values. But their particular choice of a function which values being in jail over harming others via crime is completely subjective.
It is beneficial to be able to separate these two components because there may be (and likely is) many cases in which someone is objectively poor at maximizing their utility function and it would be beneficial to steer them in the right direction without getting bogged down in their choice of axiom.
None of this is about ‘avoiding being punished for breaking arbitrary rules’, it is about maximizing expected utility, where the definition of utility is subjective.
There are many evolutionary and biological reasons why people might have similar subjective axioms but there is no justifying a particular subjective axiom. If you claim there is, then take the example of a psychopath who claims that “I do not value life, humanity, community, empathy, or any other typically recognizable human ‘goods’. I enjoy torturing and murdering people, and do not enjoy jail or capital punishment, therefore it is good if I get to torture and murder with no repercussions” and demonstrate how you can objectively prove that most extreme of example statements false. And if you find that task easy, feel free to try on any more realistic and nuanced set of justifications for various actions.
The law is the product of many individuals each with different subjective axioms separately trying to maximize their particular utility functions during the legislation process. As a result the law as written and implemented has at best, an extremely tenuous link to any individuals morality, let alone society at large’s morality. Murder is illegal because for biological reasons the vast majority of people assign large negative value to murder so the result of legislators minimax procedure is that murder is illegal in most cases.
But if an individual did not assign negative value (for whatever reason) to murder how would you convince them they’re wrong to do such a thing? It should be easy if it is objective. If you can’t do the extreme cases then how can you hope to address real moral issues which are significantly more nuanced? This is the real question that you need to answer here since your original claim is that it is objective. I hope you’ll not quote snipe around it again.
I’m not arguing general rules from exceptional ones, I’m not proposing any rules at all. I am proposing an analytic system that is productive rather than arbitrarily exclusionary.