Ignorance and bigotry aside, the notion of a Federal Marriage Amendment is incredibly stupid.
It occurred to me recently that such an amendment would impinge on freedom of religion (more on this below). Here's what the proposed amendement says:
Marriage in the United States shall consist only of the union of a man and a woman. Neither this constitution or the constitution of any state, nor state or federal law, shall be construed to require that marital status or the legal incidents thereof be conferred upon unmarried couples or groups.
If it's been a while since you've read the amendments to the U.S. Constitution, take a quick look and see if you can figure out why the one above doesn't quite fit in...