I'm by no means a Constitution authority, but my impression is that the existing amendments are all about granting rights. The prominent attempt otherwise in the past, was the later repealed amendment prohibiting alcohol. We know how that one worked out. Now the Christian right is pushing a new prohibition amendment.
I don't think the marriage amendment has any chance of making it though the rigorous process that is the route to becoming part of the U.S. Constitution. You will not even come close to getting the required number of states to ratify it.
As a side discussion, I wonder what happens if an amendment is ratified to become part of the U.S. Constitution, and it conflicts with a pre-exiting part of the Constitution (ie. Bill of Rights). I presume the later law overrides the earlier law.
Perhaps the Congressional/Presidential passing of the marriage amendment might work out to be a good thing. Send it out to the states for ratification consideration. I think the resulting uproar will be a serious blow to the Christian right, and the neo-con movement in general.
Moose
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"The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness." - John Kenneth Galbraith