polygamy?

Katherine Kersten is at her inflammatory best this week in the Star Tribune (and how she still has a job there is beyond me). It's the age old argument against gay marriage:

But wait. What if a person loves two people, or three or more? If "one man-one woman" is a discriminatory limitation on the choice of a life partner, on what grounds can the state logically restrict marriage to two people? The fact is, once you adopt same-sex marriage -- legally changing the standard for marriage from one-man, one-woman to a "committed relationship" -- there is no principled way to prevent its extension to polygamy or other forms of "plural marriage" or partnership.

This argument is really completely invalid. Why? Because she fails to outline the reasons that polygamy shouldn't be legal. The problem with polygamy is not that it is an assault on our traditional values, or somehow in bad taste. The problem is that it's very strongly correlated to abusive and incestuous relationships. If you just think about the power dynamic at play when one man is married to several women, this makes complete sense. This logic does not at all apply to same sex marriage. There is no evidence of negative effects of gay marriage except for vague claims that it "weakens the institution of marriage."