Beyond the risk of blurring intrinsic gender differences, there is a real danger to calling other human relationships marriages. It is reasonable to assume that, if we grant marital status to same-sex relationships, then other kinds of relationships, e.g. polyamorous groups, non-exclusive sexual partners, and platonic friends, will seek classification as marriage. Once the definition of marriage is expanded, there is no logical end to the vast number of various kinds of relationships that will claim the “right” to be viewed as marriages. Inevitably, the very word relationship will, for all intents and purposes, be equated with the word marriage, for there will be no distinguishing between the two. And when every kind of relationship is a marriage, what is marriage?
When marriage means everything, it really means nothing.