If the law allows polygamy, then the law should also allow each additional spouse to be a tax deduction.
So, one would then expect people to enter into fake marriages strictly for tax reasons.
If the slope isn’t slippery enough, throw some grease on it.
actually, let's ditch the tax code that dictates public policy instead. In fact, marriage is supposed to be a religious union. Gov't should have nothing to say in the matter, and the law should recognize such. Civil unions are for contractual obligations.