If I were a Supreme Court justice (God forbid), I would say government doesn't belong in the marriage business at all, and most especially it doesn't belong in the sanctity-of-marriage business. Let the various religions & nonreligions define marriage as they please. If any number of people of whatever sexes want a legally enforceable cohabitation contract, let them write it & sign it -- by & with the advice & consent of their churches, if they want. The tax code has no legitimate interest in marital status except insofar as it includes dependence, which can be defined in purely economic terms.