The solution is to end welfare, not have the Government tell consenting adults how to order their lives.
Then society should...oh wait, society has already spoken about polygamy, and found it unacceptable. And for so many good reasons. Not that they would matter to you—apparently you either belong to or support some of these vile sects that practice this. The women end up being sex slaves, literally bartered and sometimes sold to other men, often at ages under 10. The boys get kicked out on the street so as not to be competition for the drooling old child molesting geezers. This is NO life for civilized people. This is no life for Christians.