First. let us take a look at the difference between homosexuals and heterosexuals. The striking difference is obvious. Homosexuals have a sexual orientation towards those of the same sex, whereas heterosexuals have a sexual orientation towards those of the opposite sex. Why would a heterosexual woman want to marry a man? Sexual orientation. Why would a homosexual man want to marry a man? Sexual orientation. Clearly, from an individual standpoint, this is a, if not the main reason for one wanting to marry a specific other. Love, attraction, emotion. Now, this does not justify gay marriage being validated, and, in fact is a weak argument that I never make. Love, attraction, and emotion does not benefit the state, which is why marriage exists. However, polygamy does not fit well in the criteria that I have identified. There is no polygamous sexual orientation. Polygamy is, typically, a heterosexual orientation, covered already. However, being that there is no polygamous sexual orientation, using this, a mainstay of the individual reason for marriage, will not work or apply. Therefore, polygamy from an individual standpoint, does not meet the same criteria for marriage as do homosexuals or heterosexuals. Lack of orientation.
Now, we move into the societal realm. Government supports marriage for a few reasons. The productive rearing of children is most important. Creating a stable family life is also key: it adds to the positive potential for healthy children, but it also creates healthy adults. There is plenty of evidence to support the theory that those who live in a healthy, stable, committed relationship, are happier, healthier, and are more productive members of society. These are all things that benefit the state. Research shows that, regardless of sexual orientation, gay or straight, folks who live in these kinds of committed relationships, do better, and rear children better, than those who do not. This is regardless of sexual orientation. This is the second piece of the argument that will, eventually win the day for gay marriage. Polygamy does not offer the same benefits. And the answer to "why" is simple, and is psychological in nature. Jealousy, rivalry, and inconsistency. Just like my argument that psychology cannot be separated from economics, hence, because of greed, pure forms of both socialism and libertarianism are destined to be complete failures, neither can human psychology be separated from this issue. What is the number one cause of divorce? Adultery. Why? Jealousy and rivalry. In a multi-partner marriage, it would be impossible for their not to be some sort of hierarchy, and even if this is agreed upon, one cannot eliminate one's emotions. With this type of emotional instability at the familial structure's core, a healthy, committed relationship, similar to that of a single partner marriage, could not be obtained. Further, the inconsistency in caretaking responsibilities and in child rearing responsibilities, compounded by the hierarchies and rivalries will harm the children, affecting their functioning. We already see some of this in divorced families, where inconsistent rules, non-existent co-parenting, and rivalries, negatively affect children.
Lastly, though there is plenty of research that supports both heterosexual and homosexual unions as being beneficial, there is none that supports polygamy.
All of this shows how there is not correlation nor slippery slope from homosexual to polygamous marriage. Polygamy, for the reasons I identified, is not only a very different animal than homosexual marriage, but has none of the similar benefits to the state that the government currently sees marriage as.
Polygamy as a reaction to homosexual marriage is a smokescreen and an invalid comparison.
