Marriage is far more than your emotional bond with “your Number One person,” to quote same-sex marriage proponent John Corvino. Just as the act that makes marital love also makes new life, so marriage itself is a multilevel — bodily as well as emotional — union that would be fulfilled by procreation and family life. That is what justifies its distinctive norms — monogamy, exclusivity, permanence — and the concept of marital consummation by conjugal intercourse.
...All human beings are equal in dignity and should be equal before the law. But equality only forbids arbitrary distinctions. And there is nothing arbitrary about maximizing the chances that children will know the love of their biological parents in a committed and exclusive bond. A strong marriage culture serves children, families and society by encouraging the ideal of giving kids both a mom and a dad.
The authors make a compelling observation that, legally, marriage does much more than standardize a primary relationship (e.g. defaulting who ought to be your medical proxy or to whom your possession belong in the event of your death). If this was its sole function, there would be no need for the legal structure which has been built up around marriage, one which institutionalizes matters of monogamy, sexual exclusivity, and permanence. If it were about formalizing a person's primary affective attachment, it should be as easy to change as a will and open to the possibility of multiple equal levels of attachment. Which it isn't; at least not legally.
In fact, American culture has largely done away with these pillars of marital theory, particularly permanence. It is not quite as easy to change a spouse as it is to change a beneficiary in your will, but it is done with strikingly more regularity nonetheless. Sexual exclusivity is eroding with a startlingly rapidity, so that primary relationships which have not yet been formalized are rarely assumed to be sexually exclusive and even married persons have a wealth of ways to violate the bounds of sexual exclusivity with impunity. (Someone care to look up statistics about the use of pornography by married men?) Only monogamy remains largely uncontested both legally and culturally, although the authors do point out the swelling phenomenon of polyamory.
The solution seems to me to require a redefinition of marriage rather than a feigned conservative defense of the grand old institution. The heterosexual marriage characterized by monogamy, fidelity, and permanence exists more as a convenient fiction than a staid bulwark against social decay. If we care about a definition of marriage that includes these principles than a cultural redefinition of marriage is in order, one that would accord with and allow for the revitalization of marriage laws. If, however, we recognize the cultural shift behind which the law has lagged, then the legal redefinition of marriage seems to be in order, not only to exclude the heterosexual requirement, but also all laws which are artifacts of a time when marriage was permanent, monogamous, and exclusive.
My preference has, traditionally, been for the latter, but only because it divorces what is legal from what is ethical in a way that neatly accords with my view of the world. More to the point, short of a spontaneous, universal, and enduring cultural revolution that recaptures the historic conception of marriage, changing the law to reflect culture seems to be the prudent course.
(None of which, of course, comments at all on the permissibility of homosexuality in Christian ethics.)