This would arrest every state/nation so that they legally commit themselves to only relate to other state/nation as ends in themselves and thus you find yourself a Kantian statement on the level of a state/nation which can be beautiful!!! Like it?
[Added some minutes later:] The Corwin Amendment is this,
- 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.
Source is http://en.wikipedia.org/wiki/Corwin_Amendment!