"However, the uniqueness of marriage is that it embodies the underlying, objective, distinctiveness of men and women. This distinctiveness and complementarity are seen most explicitly in the biological union of man and woman which potentially brings to the relationship the fruitfulness of procreation."
The marriage service, at least in the Episcopal Church usage, does not dwell on the distinctiveness of men and women from each other, but rather on the equal nature of the two in making this commitment / contract / covenant, noting that together, if it be God's will there might be procreation and raising of children. "Biological union" is called a variety of things, but it is, let us say fleeting and not particularly a useful model for committed relationship. Biological union has little or nothing to do with the union of man and woman in marriage, except to say that sexual activity is part of the package. The pledge of being "faithful" only to the partner in marriage is the only reach into the question of the biological union and the marriage union. This first proposition also equates the distinctiveness and complementarity. It makes it seem that our distinctiveness is that we are different puzzle pieces that can be fit together. Ho hum. (see diagram below)
"To remove from the definition of marriage this essential complementarity is to lose any social institution in which sexual difference is explicitly acknowledged."
I confess that I once went to several social institutions in which sexual differences were explicitly acknowledge: an athletic club in New Orleans, where women were only allowed in the members and visitors dining room; a church where women were not allowed to be at the altar except as cleaning ladies, politely called the altar guild; a para-military organization in which women were excluded from particular activities because of the biologically determined average difference in muscular strength between men and women. All of these social institutions have gotten over the need to explicitly acknowledge sexual difference in their organizational behavior, which is not to say that they have overcome sexism.
I think it would be quite useful to remove sexual difference from the expectations and oaths taken in marriage. So does the church, which somehow determined that it was something of a biological stretch to say that the woman will obey the man, and not the other way around. Maybe the official BCP that everybody thinks is so great still thinks that one of the major reasons for marriage is to put a stop to fornication and that women are meant to obey men but not the other way around, but times have moved on.
While we are at it, it is time to stop saying this nonsense (which we in the Episcopal Church do all the time) of saying that "The bond and covenant of marriage was established by God in creation, and our Lord Jesus Christ adorned this manner of life by his presence and first miracle at a wedding in Cana of Galilee." This pushes so many buttons in the realm of both biblical studies and biblical theology as to make them laughable.
Still, it is true that men and women are differently made as per plumbing, chemical make up, distribution of facial hair and body fat, and so-forth. It's enough to make us Venus and Mars, I suppose. But if we buy this complementarity business we have to buy the rest: if the two candidates for marriage are not complementary enough they can't get married. What are we going to include? What exclude? Well, we've tried this and mostly it has turned out to be about cultural and familial norms. Sometimes the attempt to fulfill such norms have worn women out or lead to their death or divorce. (Try having to produce a male heir as part of expectations.)
"To argue that this is of no social value is to assert that men and women are simply interchangeable individuals.We believe that redefining marriage to include same-sex relationships will entail a dilution in the meaning of marriage for everyone by excluding the fundamental complementarity of men and women from the social and legal definition of marriage."
This whole thing is brought to you by someone who knows logic chopping and rhetoracle slight of hand. Complementarity is introduced. The straw-man opposition is introduced, "if you don't hold to our position you believe that 'men and women are simply interchangeable individuals'..." and then saying, "see, do that and you exclude the complementarity we are supporting." Well, sure. But two little things: (i) denying the social value of maintaining marriage as being between one man and one woman is not necessarily or always to assert that men and women are "simply interchangeable individuals." There are lots of reasons to take delight in the differences, and celebrate the joys of connecting (wink, wink) across those differences. But (nudge, nudge) that's always there, because we are all different. (ii) The complementary character of two persons as they live, love and die together is a reality that has little to do with their being a man and a woman. It is a reality that has to do with their being --- get this --- two people. Allowing same sex marriage may change our understanding of what marriage is, but there is no convincing argument that it dilutes it's meaning.
The upshot of all this "complementarity" business is a rather weak argument based on the realities that most people come with a package deal in which sex organs are well defined and psychological and physiological interests, abilities and urges are all ordered so that some are called men and other women and somethings about their bodies suggest they may be "complementary." "Complementary" means of course that the sex organs "fit" together for a clear biological purpose.
But that nifty sexual complimentarian "fit" is not enough to justify an institution like marriage as being only about one man and one woman. Marriage also requires a wide range of complementary "fits" such that men and women are made for each other psychologically, physiologically and socially. Most of what marriage supports are cultural expectations of men and women, expectations that for a particular culture may have served it well. The question is not then if the concept of marriage is diluted by allowing for same sex marriage, but if marriage is enhanced by understanding that complementarity is not about sex organs but about life hopes, vocation, desires, etc.
So here we have it. The document notes with some wonder that there are two sorts of people, innies and outies. As in:
Innies and Outies
The whole of the CofE paper on marriage falls apart as we see more and more clearly that the writer, polite as can be, confused the peculiars of outward and visible signs of difference for the realities of inward and spiritual signs of difference and complementary characteristics that really make for success in union and common life.
I have a fine life in a marriage where the external observation is one of us is an innie and the other an outie. Fortunately the real differences are shared by the two of us in ways that have little to do with being a man and a woman, but have to do with love and respect, delight, sorrow... you know the full range of the life only those committed to each other have.
This paper neither addresses marriage as I have experienced it or marriage as I support it. Read the paper again. Here is the link. Does it for you?