The problem that I see with your approach Keg, is that from where I stand, it appears that you try to use logical argument to support a view that you have already formed. My view is that you can use a rights based approach, or a utilitarian ethics based approach, and 'discover' the answer. I genuinely meant it when I stated I had not turned my mind to the polygamy question. I am happy to apply a utilitarian approach to rights and accept what answer emerges. Either way. I have not pre-determined an answer that I have to twist an argument to achieve. As I stated, my personal observation of polygamy was associated with the denial of rights for women. That may be a universal consequence of polygamy, or it may not. Let the discussion occur if it really is an issue. I am not afraid of the answer either way.
Regarding the rights being denied on either side of the same sex marriage debate, I don't agree with the arguments that state that current marriages and families will have their rights denied by allowing same sex couples to marry. This disagreement is not just uninformed opinion, but the result of formal research on the subject. So, on balance, the question of SSM is that of denial of rights not allowing it, with no associated denial of rights by allowing it. Polygamy is a more complex issue. My concern is not so much about how allowing it would affect the status of my marriage, but what rights would be affected by those within the polygamous marriage.