I agree with both of you about same-sex marriage, and in response to Post 2, I would make this argument. Same-sex marriages and "traditional" marriages both involve two consenting adults, who are mutually agreeing to enter into a legal contract in which both are equal partners. In case of polygamy, at least as defined by our legal system, this is not the case. One man married to multiple women is not an equal partnership, as it privileges the man. For that matter, polyandry would privilege the woman, or, depending on the situation, the man. Similarly, a child entering into a marriage with an adult (to cite another example of the "slippery slope" argument often made by opponents of SSM) is not an equal partnership for obvious reasons.