Who said that that new definition of "civil union" has to be limited to two people?
But just wait 'til someone comes and wants to marry his horse, his bed or his imaginary friend.
A horse, bed or imaginary friend can not enter into a contract. My dog, who I love very much, is incapable of entering into a contract, she lacks the understanding of her actions and I am basically her legal guardian because of her inability to manage her own affairs independently. I signed up for this job with that clearly understood, it would be an abuse of my duty as her guardian to force her into a contract that she is incapable of understanding. Just the same for my desk, who I spend almost as much time with as my wife, can not enter into a contract with me. My desk can not read, understand a spoken topic and the consequences of a decision (same for my dog). On the other hand, two adult humans or groups of them who love each other can clearly consent to such an agreement. Its not our place to judge the basic competence of other adult humans to enter into agreements with others similarly situated.