"that states should have the final say over the legal status of personal relationships. "
But that isn't what is happening currently. The legalization of gay marriage in one state would have the effect of legalizing it in every state.
Gay couples will get married in say Mass., then move to another state (say Montana). Montana would then be forced to recognize the gay marriage due to the full faith and credit law in the constitution.
Gay couples can't get married in every state, but their marriages must be recognized by every state. Essentially stripping each state of the ability to decide this issue for themselves.
That's nonsense. If Montana doesn't issue (for example) drivers licenses to anyone under 25, then no one under 25 drives, and that includes anyone under 25 from another state who moves there with a valid license from the other state. The license from the other state is useless in Montana. A license for any imagined activity, illegal in Montana, legal elsewhere, isn't going to hold any weight in Montana. The full faith and credit clause was never intended to force a state to permit illegal behavior just because that behavior is legal in some other state.
This whole idea of preemptively amending the Constitution is hysterical madness. The federal courts are going to decide this matter before this stupid amendment ever gets passed anyway. Sheez, the things people worry about.
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Article IV
Section I
Full faith and credit shall be given in each State to the public acts, records, and judicial proceedings of every other State. And the Congress may by general laws prescribe the manner in which such acts, records, and proceedings shall be proved, and the effect thereof.
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Therefore, a competently written Federal Defense of Marriage Act is all that is Constitutionally required to bar the spread of homosexual faux-''marriage'' from Mooseapoopetts to other states. Such an Act would simply have to provide that the ''effect'' of allowing this bizarre ''marriage'' in any State is limited to that single State. Upon such limitation at law, every other State would indeed be obeying the Constitution regarding ''full faith and credit'' by merely ignoring such ''marriages'', for their ''credit'' (which in context means ''legitimacy'') would be defined as nil outside the issuing state, by law -- much in the same manner as, I might note, the assorted concealed-carry laws are right now, and WITHOUT benefit of a Federal statute for justification.
On a different branch of this topic -- Regarding whether or not this subject is a matter of states' rights, as per the 10th Amendment, at the moment it is such. However, the 10th uses the formula ''Powers not granted to the United States by the Constitution...''. Clearly, from the text, if the several States so desire, whether subsequent to a Congressional Act or a Constitutional Convention, to ratify an Amendment and thereby do in fact grant this power (of regulation of marriage) to the United States, then no longer would ''states' rights'' be relevant to the discussion.
Sadly, because Federal courts have for many decades ignored the plain text of the Constitution, I consider it highly doubtful that these completely straightforward and contextually accurate arguments will prevail at law.