"It is the courts that have illegally amended the constitution. Not the Christian Fundamentalists."
Oh ok, so where did the courts unlawfully define marriage in the Constitution?
It's complicated. Lets just say that it has to do with the full faith and credit clause. A marriage that is valid in any state is valid in all states conferring upon that couple all rights and privileges that would be available to any other married couple.
If the state courts start finding some constitutional right to homosexual marriage or incestuous marriage or polygamy, then in order to prevent some state like Massachusetts from imposing its homosexual marriage or polygamy laws or child marriage laws on other states, a constitutional definition of marriage is needed. Thus if Massachusetts suddenly decides that it wants homosexual or polygamous marriage, then New Hampshire doesn't have to recognize that marriage.