Aside from offering that theory, I want to quickly dismiss the authors assertion of the conjugal theory of marriage. He writes:
but they marry in order to make something new that honors and ennobles that attraction and love: the nucleus of a family, in a comprehensive relation of husband and wife that points toward the future, with an openness toward making that future through procreation.From what I've seen and read, this is not the current mainstream attitude towards marriage. Instead, marriage is an expression of romantic love and commitment. What I learned in history class is that this romantic theory of marriage gained prominence in the 1950s and was largely the norm by the late 1970s (at least among the college-educated middle-class). Within this context, childbearing is an exciting opportunity offered by marriage, but definitely not the point of marriage.
To say that there is no reason for formal recognition of the household in the absence of childbearing is silly (and I won't give any attention to semantic quibbles over the word "marriage"). We have standard legal recognition of many arrangements, including business partnerships and corporations. Why not a household? Why not give a special place to a union of two adults. And no, the recognition of gay marriage does not imply that we should also recognize threesomes -- there is a major, consequence of the union of two people which is not comparable to the effect of adding a third*.
Anyway, it's not all that surprising that gay marriage has suddenly become an issue, and it's not all that radical given the preceding changes to our conception of marriage and the mainstreaming of homosexual relationships. In many ways, it is just the cherry on top.
*Okay, upon more thought, maybe my logic would allow for the recognition of threesomes (but not larger groups). The problem with recognition of pairs only is that if a threesome were to form, then one member would not have any recognition of his relationship.