In the past, and present for a few cults, polygamy has been based on subjugation of the female participants. IF and it is a big IF, there were protections for those who chose to live in a polygamous marriage then I too can see polygamy being legalised. A major problem for the American fundie cults that are presently practicing polygamy is their treatment of male youth, too many of the boys are thrown onto the street so that the better connected, mostly older, men have more females to choose from.
Then how about those women who choose to have multiple husbands? Would they be covered by the same laws that allow multiple wives?