
Originally Posted by
Gingersnap
There isn't any. Marriage is a consensual contract that is recognized in law. Any 2 people (or group of people) are perfectly free to enter into a contractual agreement that covers inheritance, property rights, powers of attorney for financial matters and health issues, and other things.
What they can't do is apply for certain government benefits or pension benefits on each other's behalf.
I expect that entire issue will go away shortly as more people favor domestic partnerships that have nothing to do with sexual expression. Marriage will return to the private sphere and religiously married couples will also have to take out a domestic partnership.