... no principle that argues against incest and polygamy.
You know those opponents of marriage equality who said government approval of same-sex marriage might erode bans on polygamous and incestuous marriages? They’re right. As a matter of constitutional rationale, there is indeed a slippery slope between recognizing same-sex marriages and allowing marriages among more than two people and between consenting adults who are related. If we don’t want to go there, we need to come up with distinctions that we have not yet articulated well.The left is in this bind in part because our arguments for expanding the marriage right to same-sex couples have been so compelling. Marriage, we’ve said, is about defining one’s own family and consecrating a union based on love.//
Welcome to Civilization 3.0, where everyone is so much wiser because they have the internet.