The slavery ammendment, having now nothing to do with slavery, is great.
The amendment states:
No amendment shall be made to the Constitution which will authorize or give to Congress the power to abolish or interfere, within any State, with the domestic institutions thereof, including that of persons held to labor or service by the laws of said State.
What are the "domestic institutions" of a state? The amendment strikes me as excessively vague, and might have become a pretext for judicial activism, just like the due process clause. Moreover, it restricts future constitutional amendments, thereby reducing constitutional flexibility.
Marriage certainly would fall under the domestic institution proviso, but I agree that clause is rather vague and subject to interpretation, and the zero admendment part gives me the willies since there would be no recourse other than revolution if a Supreme Court ever misinterpreted it. The right of revoultion is a necessary and proper right, but we should never structure our laws such that it may someday become necessary.