The federal definition of marriage is little more than a means of bribing the people through a tax definition.
Its a tax deduction like one on home loans, a probably a better one. And certainly a better than GWBs single Mom tax credit, which would stand BTW.
In some cases getting married actually costs y MORE in taxes than singles living together in sin. Here in Maryland Federal AMT does that to middle class where both in married couple work professional jobs, because combined income triggers it.