bls commented: "people who don't want children CAN marry, and the grammar is "marriage." There is, literally, no difference whatever between the marriages of elderly couples and those who are planning families; they are exactly the same in law and in fact". I want to engage with this a bit more formally, at the risk of completely compromising the order in which I wanted to address things (!)
I have long believed that the situation that we are in now is a result of changes in our society triggered by the advent of easily available and reliable contraception. The consequences of the development are complex and many-faceted, but one is the recognition and affirmation that there are at least two key facets to sexuality - one "for the mutual society, help, and comfort, that the one ought to have of the other, both in prosperity and adversity", and one for the procreation of children (I'm ignoring, for now, the 'remedy against fornication' aspect which seems to me to be more puritan than Christian).
The legacy that we have, however, comes from a time when those two elements were understood to be united, and, moreover, combined with questions of inheritance and honour. So a marriage was often not simply about the union of two individuals (for whatever motive) as about the union or explicit political alliance of two families. The raising of children was (legally) kept within the bounds of marriage, with significant consequences for both the mothers and children of those born 'out of wedlock'. In many cultures that remains the case of course.
Given this, the only way in which an affectionate union could be legally sanctioned was through marriage; and when such a union was so sanctioned, the approval carried a vast array of social weight. It seems to me that THIS is what the proponents of 'equal marriage' are seeking; in other words, it is all the weight of social approval embodied in the word 'marriage', as accumulated through history. It would represent, perhaps, a culmination of the 'coming out' process. In so far as this is what it means then I am wholly in favour of it.
However, this is where we get snagged upon semantics. For it seems to me that this aspect of marriage functions rather in the way that Stephen Jay Gould talked about 'spandrels'. That is, the primary purpose of the social institution of marriage - and, I would argue, the reason why it has been regulated so closely - is the raising of children within a particular framework. That is the 'core' element of marriage, as understood. However, as the institution has developed, other elements have gone alongside it - elements that 'came with the package' where the union was reproductive, but which developed independent status as social goods in their own right. These 'exaptations' now need to be given their own autonomous social place.
So much of the opposition to gay marriage is rooted in an opposition to homosexuality as such. I am not part of that; in so far as the gay marriage agenda is about giving wholehearted social approval to gay relationships, that is (obviously) a good thing. Yet it seems to me that by insisting that non-reproductive unions ARE 'marriage' (which, as bls rightly points out, non-reproductive heterosexual unions have been so treated thus far) the difference between the two key facets - and, most especially, the fact that society has a significant greater interest in the raising of children than in the mutual society of a couple - is being eclipsed. That is the essence of my unease with what is happening. I think that a significant good - all the social apparatus around the raising of children - is at risk of being dismantled in favour of another good - the social approbation of gay relationships.
Where I disagree with bls is that I think that there is a major difference (in fact if not in law) between a couple that are procreative and a couple that are not. Indeed, to insist otherwise is to obliterate the pain of childless couples - for if there is no difference, why do they mourn? And I believe that the wider society (and God) takes a different view of the two forms of relationship. We have not yet worked out how to navigate this difference (doing so is the purpose of my TBLA sequence) and it may well be that, simply as a result of our biology, it makes no sense to separate the two. Or, it may be that we need to develop two new institutions to replace the old one of marriage - call the first 'covenant relationship' and the second 'coparent relationship' perhaps? I think that there is a difference between these two forms of relationship. Can both be adequately described as 'marriage'? Possibly, but I just don't think the case has properly been made yet.
Oh yes, and, for what it's worth, I think that the CofE being prohibited from carrying out gay weddings is the worst of all possible worlds. Cameron is such a plonker.