Should Polygamy be legal? Please support your answers with reasons, not sources of authority.?

By asking people who wish to answer to support their arguments with reason and ysis, I hope to deter people from saying, "polygamy should be illegal because it has not been recognized as a traditional form of Christian marriage." This answer is no good for me. Though it may be a good answer for people who share your beliefs (and that may be dubious), it will not convince someone who doesn't share your religious convictions. So, please support your answer with ysis and reason.