"No one wants to say that any interpretation has validity."
This you assert, but then you immediately contradict yourself:
"But practically speaking establishing objective limits is not possible - they have no meaning except an operational one; whatever the Supreme Court says is a valid interpretation is one."
You are saying not that any interpretation is valid but that any interpretation of Supreme Court Judges is valid. You admit they are tyrants. Whatever they say is law. What you assert is that no longer is the Contitution the Supreme Law but rather any Utterance of the Supreme Rulers. Using that logic I could ask: who then is to say what the Supreme Court means in their opinions. You see it is a slippery slope, nay it is a precipice or rather the abyss into which we plunge.
Now do you understand my argument? When Holmes began debating the meaning of meaning, he poisoned the law and language. The result to which we are witnesses is confusion. And we grow more and more confused so long as Holmes' "interpretation" of interpretation is considered legitimate.
I won't discuss Holmes' philosophy with you because I don't feel competent to do so. But I am in agreement with his general idea that each generation decides what is moral and legal. That absolutes are difficult if not impossible to capture.