The ultimate foundation of law has to be truth. Law has to rest on what is actually so. If it isn't true, it can't be law.
So before we can talk about law at all, or about any of the problems facing our world and their solutions, we have to agree on one statement. It is the basis of every honest discussion:
Objective truth exists.
We don't have to agree on what it is
"But people have different versions of the truth. What if people disagree about what the truth actually is?"
They do, all the time. People disagree constantly about what the truth is in a given situation. But to disagree about what the truth is, you first have to accept that there is a truth, sitting there, waiting to be found or deduced. Otherwise there is nothing to disagree about, and nothing to be wrong about.
We don't need to agree on a particular set of facts or interpretations in order to have a responsible discussion. We only need to agree that the truth exists, whatever it turns out to be, even if no one has found it yet. Then we can get to work finding it.
And this much is not really open to dispute. The statement "objective truth does not exist" is itself a claim of objective truth. It refutes itself the moment it is spoken. A self-contradicting statement cannot be the foundation for anything, least of all for morality and law.
Not every truth is objective, but some are
"What about truths of personal feeling? Art, music, poetry, beauty, the things we can't put into words? Aren't those subjective, different for every person?"
Perhaps they are. Not every truth has to be objective for some truths to be. Whether a song is beautiful may well depend on who is listening. That has no bearing at all on whether truths about morality and law, rights and dignity, are objective. One kind can be subjective while the other is objective. That is possible. And it is so.
Truths about art, poetry, and beauty may be subjective.
But when a truth concerns rights and dignity, it is objective.
An example: race
A person's race or color confers neither superiority nor inferiority. It does not change the dignity a person is owed. Everyone deserves equal treatment before the law, regardless of race or color, and any "law" that discriminates on that basis is unjust, immoral, and, as we will see, not really law at all.
That is an objective truth. It does not depend on the feelings of anyone who happens to be prejudiced. A bigot can feel, subjectively, that people of other races ought to have fewer rights. He can feel that as strongly as he likes, and call it his "personal truth." But objectively, his belief is false. Not merely unkind, not merely socially maladaptive, but factually, descriptively incorrect, in the same way that a wrong answer to a sum is incorrect.
Consider what would follow if it were otherwise. If truths about rights and dignity came from personal feeling, then anyone who personally felt it was acceptable to hurt people for their skin color would be justified in doing so, because that is "their truth." Or if such truths came from collective feeling, then the moment enough bigots made up a majority of the voters in a society, bigotry would become true. Thank goodness truths about rights and dignity don't work that way.
Why it is true
Here is the crucial point. The reason everyone is entitled to equality before the law, regardless of race, is not any social convention or institution.
It isn't true because a government outlawed racial discrimination.
It isn't true because a document like the Declaration of Independence says so.
It isn't true because society has evolved.
It is true because it is true. You do not deserve less respect because of the color of your skin. That is a fact, not a social agreement: a descriptive fact about reality. Governments, documents, and social progress can recognize that fact, or fail to. They cannot create it, and they cannot abolish it.
All truths about morality and law, rights and dignity, are objective, sourced in reality and nature, not in personal belief or social custom. They stand independently of thoughts, feelings, ideas, prejudices, customs, cultures, agreements, proclamations, and documents.
Morality has to be something no one can edit
There is a second way to see that morality must be objective. Ask what would happen if it weren't.
If human beings had the power to edit morality, to change the definition of right and wrong, then any evil could be justified simply by redefining evil. Anyone who wanted to commit an atrocity would only need to adjust morality's definition to match the thing they wanted to do, and then go ahead and do it. Morally.
That is the unavoidable consequence of a morality we control. And plainly we don't control it. Morality's definition lies beyond our reach. All we can do is choose whether to follow it. We cannot change what it is.
All of law works this way
Equality before the law is one example, but every true principle of law works the same way. Every detail of the law rests on objective truth. It has to, by definition: a rule that does not rest on objective truth is, by definition, not law.
Every detail of the law can and must be linked to objective truth, and built firmly on it. Every detail of the law is an extension of logic, beginning from objective truth.
Including the Law of the Earth itself
Everything written in the Law of the Earth aims to describe what is objectively true. We say "aims" on purpose. It is always possible to misidentify a truth, and we must stay open to that possibility. However carefully we reason, we still make mistakes, and somewhere in this work there may be an error. To claim otherwise would be intellectual totalitarianism, and intellectual totalitarianism leads quickly to the real thing. We will never claim this work is perfect.
But if there is a part you think is wrong, you have to use reasoning to show it. "I don't agree. This is baloney. Who gave you the right to say what the law is?" is not an argument. If you believe something here is mistaken, say why. Point to the flaw in the reasoning that leads to it, if there is one. And if there is, we want to hear it. That is how understanding grows: someone finds the error, the error is corrected, and the next version is more accurate.
Truths about rights and dignity are objective and consistent. One person's rights never depend on another person's feelings in the moment.