The right to marry doesn’t come from your neighbors, or society, or President Bush.
This isn't the reason we have a constitution. Our Constitution defines the form and function of government; it's not a document for defining our interpersonal relationships. For example, the Constitution establishes the three branches of government: executive, legislative and judicial. It establishes the make-up of Congress. It reserves the power to print money to the federal, rather than state, government.
The 12 original amendments to the U.S. Constitution were known, collectively, as the Bill of Rights. There are now 27 amendments. The Bill of Rights is consistently misunderstood. People often think that this document grants Americans their freedom of speech, freedom of religion, right to keep and bear arms, freedom from unreasonable searches and seizures of property. It does no such thing. The document presumes that freedoms in all these areas already exist. We are literally born free, in the eyes of the Constitution. The Bill of Rights protects our freedoms not by granting rights, but by prohibiting the federal government from infringing on those rights. Subsequent amendments typically identify in finer detail which pre-existing rights the government may not trample. For example, the 19th Amendment didn't "give" women the right to vote, it stopped the government from keeping women away from the ballot boxes. (See www.usconstitution.net for plain-language explanations of the whole document.)
Why is Bush's proposal bad Republican behavior? First, it's inconsistent. Republicans can be downright constitutional literalists when defending, say, the Second Amendment. However, in this case, Bush's proposal perverts the purpose of the Bill of Rights, turning it into a document that limits freedoms instead of protecting them. The right to marry doesn't come from your neighbors, or society, or Bush. It comes from your own autonomy to find somebody you think you can stand for a few decades, or at least a long weekend in Vegas, look them square in the eye and say "I do."
The only other amendment that tried to buck the function of the Bill of Rights in order to control citizens' behavior was the amendment authorizing Prohibition-a disastrous misuse of the document that was ultimately repealed.
Second, the constitutional amendment is specifically meant to trump states' rights, which Republicans otherwise champion. Bush explained that he was worried "activist judges" and liberal states would authorize gay marriages that other states would then have to recognize under the Constitution's "full faith and credit" clause. (What are we supposed to do about activist presidents, I wonder?) However, as recently as his 2000 campaign for the presidency, Bush was firmly in keeping with Republican tradition by insisting that it was up to the states to decide issues such as gay marriage for themselves.
Finally, Republicans constantly promise a smaller, less intrusive government, one that stays out of the private lives of its citizens. Telling us who we can and cannot marry is the opposite of that. It interferes with our own private hopes and aspirations, it compromises the freedom of citizens to enter into voluntary private contracts.
The federal constitutional amendment is not a done deal. But in Hawai'i, something similar already is. In 1998, Hawai'i voters amended the state constitution so that "the Legislature shall have the power to reserve marriage to opposite-sex couples." Indeed, state law does now specify that a valid marriage contract "shall be only between a man and woman."
Hawai'i's view on this teeters around the 50/50 mark. For example nearly half of people responding to a Honolulu Star-Bulletin poll disapproved of Bush's proposed constitutional amendment. But we've already jiggered around with our state constitution. Two citizens can come before the state and say they want to get married. Under our state constitution, if they're the "wrong" kind of citizens, the government tells them no. That's what you get when you don't have a strong constitution-life, liberty and the pursuit of happiness, except where prohibited by law.