> Appealing to the Constitution isn't really a valid line of argument, though.
I disagree. Right or wrong, it is the document against which we supposedly make all laws. I'm not suggesting that we appeal to it as it is, rather, appeal to its defined measures for ensuring that it is kept current. Put simply, in football, they have a rule book. That rule book is what we consult on matters of the rules. Sometimes they get it right, sometimes they get it wrong, and sometimes the rules need updating -- but suggesting that we disregard the rule book while playing football seems naive. The rules are necessary.
The Constitution is that rule book. Either follow the rules or write new ones. Why is that so untenable?
> The Constitution isn't the Bible. It cannot, and should not, prescribe morality, which is what should drive law-making;
I disagree that law-making should be driven by morals. The Constitution, in theory at least, should work as a bulwark ensuring that minority opinions are upheld. Just as homosexuals are fighting for equal rights under the law because their moral values aren't shared by enough people, the Constitution is their prescriptive measure. They have equal rights because they are people, and deserving of equal rights, regardless of their or others' morals. We're still niggling over the details of it, but ultimately, I have hope and faith that gay rights will eventually achieve parity in law that the rest of us enjoy.
> nor should any part of it, including the Bill of Rights, be sacrosanct.
... until it is ratified, I disagree.
> The Constitution, and its derivates the US Code and state constitutions, are authoritative only to the point that they usefully represent their constituents' morality.
Perhaps I'm misinterpreting the statement, but by your argument, gays shouldn't have rights if the majority of constituents agree they shouldn't? I disagree here, and I would expect that every minority group should. It's very possible that I've misconstrued your intent though, so please feel free to correct me if I'm in error.