I would contend that systems of morality are "real" to the same extent that customs are real, traditions are real, rules of etiquette are real, and rules of thumb are real. If you are insisting upon some sort of physical existence, then, of course, none of these is "real."
None of them are "real". All have the same basis, with the possible exception of rules of thumb. Morality, customs, traditions, and rules of etiquette are established by tradition, and cannot be established other than by common agreement that they are "true". Which, in the sense of having a physical reality, they are not; and because they are not "real", principles of morality (or custom, or tradition, or etiquette) become impossible to establish except by common agreement.
You had said previously: "...I find no compelling arguments for the rightness or wrongness of any particular principle; a precept is right or wrong merely because we say so. (Or because God says so.)" To which I replied: "What if I say you're wrong." In response, you asked me to identify one system of morality that wasn't arbitrary. Very well: your system.
Except my system is not a system. As I said (and you agreed), moral relativity offers no means within itself by which a moral system may be evaluated.
After all, you've already admitted to an objective standard of right and wrong (or, more accurately, correctness and incorrectness): otherwise, you wouldn't have asked for proof that you were wrong. And if one can be objectively correct regarding a fact, presumably one can be objectively correct regarding morality. If, however, that's not the case, then you need to explain how one can be objectively correct about some things but not objectively correct regarding morality.
I agree there are objective standards in many disciplines. I don't happen to think morality is one of them. If you can establish an objective standard for a moral principle, then I am wrong. But I don't think you can do it. And I don't believe it is incumbent upon me to establish that moral laws should have the same footing as physical laws when its clear to me they don't.
If "toleration" is a higher-order good than something else, then toleration is morally preferred. For instance, if I have a duty to denounce lies, but I have a higher-order duty to tolerate liars in certain circumstances, then there I am being morally consistent by not denouncing a lie in that circumstance.
This sounds like situational ethics to me, but also something of a corruption of the concept of tolerance. How would you state your principle of tolerance so that an ordinary citizen would know when to apply it, and when not to?
But that's not philosophy. What you're describing is, at best, sociology.
This is really the heart of the matter. For those who accept the concept of moral relativity, philosophy needs to take a back seat, because sociology and anthropology are more relevant.
The moral relativist doesn't merely say "this is what is done" but rather states "this is what should be done." Moral relativism is, at its core, prescriptive, not descriptive.
I have no clue what should
be done; and, in spite of centuries of philosophical systems that claim otherwise, neither does anyone else, at least in terms of establishing an objective system. We have moral guidelines established through trial and error, by custom, and by tradition; and, in a world which is becoming more unified, some movement toward a unified code, which, like all the disparate codes it may come to replace, will be arbitrary, based on the needs and perceptions of the people who follow it, and subject to change as conditions and fashions change. Philosophers are merely the tail trying to wag the dog, along with religious leaders, politicians, and social activists, but the beast will defy all attempts at finality, just as hidebound conservatives will resist all attempts to assert that it is not already finalized.
---as my schedule will preclude spending much time here for the next two or three weeks, I cede the final reply to you, joe, unless someone else wishes to take up the cause in my stead. I've enjoyed our exchanges. Although I'm sure no opinions have been changed, no one have been hurt by the process either.
---Although apparently some of the other natives are a little restless...I'm hopping down from the soapbox now.