Polygamy should be de jure legal, as it is already de facto legal. If an individual is allowed to have two girl-friends at the same time, then why can't he be allowed to have two wives? At least marriage means that the person will have to show some responsibility towards his wives and children, in case they breakup.
In case of a divorce or inheritance who gets to keep the kids, the house? How does that work in polygamist societies?