My response is mixed. I don't want to take things back to first principles everytime I argue, but if we're talking about the foundation of the law, it seems that everyone goes back to something larger and more fundamental:
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.--That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed...Or:
Whereas recognition of the inherent dignity and of the equal and inalienable rights of all members of the human family is the foundation of freedom, justice and peace in the world,Which as far as I can tell means that there's something analytic about their judgment. Contained in the definition of 'human' is "deserving of free health care", apparently. I disagree, but then that's Proclus' point: that no argument can be undertaken unless certain postulates are assumed. I can't argue with the UN Declaration of Universal Nonsense unless I do so on their terms.
Whereas disregard and contempt for human rights have resulted in barbarous acts which have outraged the conscience of mankind, and the advent of a world in which human beings shall enjoy freedom of speech and belief and freedom from fear and want has been proclaimed as the highest aspiration of the common people,
Whereas it is essential, if man is not to be compelled to have recourse, as a last resort, to rebellion against tyranny and oppression, that human rights should be protected by the rule of law,
I could, for example, point out that if everyone deserves health care and free education, this means that there must always be a certain number of doctors and teachers. If the market won't supply them, for whatever reason, the government steps in. Oppressive taxation? Oops! Article 17. Force? Article 23. These 'positive rights' are not rights that I can possess by myself; they depend on a society around me for their very existence. And so they cannot emerge from the analysis of the concept of a 'human', unless we include within that concept the concept of 'society'. Which does not seem tenable to me, since it's quite easy to imagine a man without others around him. I believe it was Charlton Heston. Existence is not a predicate, dammit!
Distracted; back to the argument at hand.
I think, though, that the number of bases for law is limited. People won't obey laws when they'd be better of in a state of nature, as Rousseau points out. So laws can't oppose human nature to too great an extent, or they'll be ignored. I presume I need not bring up examples in history, which are innumerable.
People tend to base their laws on two things: God, or 'fair-play', which could here be interpreted as making sure that oneself is not oppressed by making sure no one else is as well. Either way, we're claiming that human nature itself is opposed to something (the King of England ruling his colonies) or demands some action (free health care). Mandates from the masses don't even make the list. The masses have mandated any number of things that have crashed and burned rather spectacularly.
I am not aware of the failure of any system of law which was based on farcical aquatic ceremonies.
I am far from claiming that bad laws--based on someone's idea of God's will or justice--have not been made and followed. But the very idea of a 'bad law' presupposes some basis for criticism. If we're not getting our laws analytically, we can't even complain if some of them are contradictory. But I am claiming that laws which cannot be followed, will not be (a necessary conclusion). And so we will not long have laws which are opposed to human nature. This nature also provides a positive basis for creating laws: they cannot be contradictory, since our reason won't stand for it (well, most people's reason, I hope); they must address some need possessed by men.
The argument that laws simply provide an arena in which men may struggle seems to me to collapse as well. It doesn't answer the question of why they should choose law, as often and as regularly and as eagerly as they have throughout history, instead of force, or Tortoise Oracles. I, for one, would be perfectly happy settling most of my legal disputes with a pointed stick. It would cut down on my speeding tickets immensely. But law claims, and must claim, in order to achieve that superiority it seeks, that its basis is firmer than that of force, or even Tortoise Oracles. Its claim against these others cannot be in the field of law, since the establishment of law depends on this claim, and must rest outside of the law itself. Simply because the analysis of this claim is more difficult without plausible artificial postulates is no excuse for refusing to undertake it.
I will be the first to admit that laws are often passed because they meet some need possessed by a man, or a small group of them. Human nature is far from perfect, in reason or in morals. This imperfection is often passed on to the things we create, even as we create them in the hopes that they will alleviate it. But I do think that the unrelenting lathe of history tends to remove such laws as are profound injustices. Whether this is evidence of a benign deity or the evolutionary advantage of morality is up to the reader.
I should point out that I am an optimist. I believe that this stupid farce we call the "War on Drugs" will end soon, and that law will eventually be a protector of truly fundamental rights, instead attempting to achieve some earthly eschaton.
Post-script: I had no idea Charlton Heston was going to be in a movie about Genghis Khan.