I once read a novel that favorably depicted group marriage, between two or more men and an equal number of women, as a responsible and satisfying arrangement.
Such a practice would obviously violate polygamy laws, and pronouncements that marriage is between one man and one woman. Yet it seems not to entail the inequality issues that Marci discusses regarding traditional polygamy.
How would the constitutional argument go in such a case?
Polygamy has been on the decline worldwide because it is an inherently dysfunctional system that requires multiple women to be co-equal to a single man, the abandonment of a certain number of boys to eliminate competition for women, and resort to younger and younger women. It is also economically impossible to maintain, which is why the polygamous subcultures in the US rely heavily on welfare (and feature undereducated women and children). State legislatures have tremendous resources to justify the ban.