In all this, however, there seems to be no agreed definition of what marriage is.
What you call it is part of it, but even that does not seem to have been thought through.
"Gay wedding" is a misnomer. "Gay" is an adjective that applies to people. It refers to a person's sexual orientation, that is a person who feels sexually attracted primarily to people of the same sex. But when "gay" qualifies "wedding", doesn't really mean a sexual orientation of a person, but the character of the wedding itself -- carefree, happy, joyful. I believe my wedding was gay.
It is not gay weddings, but homosexual marriages that are the issue, that is marriages where the parties are of the same sex.
For many people the concept of "homosexual marriage" is a contradiction in terms. Britain has dealt with the situation more sensibly than South Africa, by not trying to pretend that it is marriage, and that what they are registering are civil partnerships.
But perhaps the solution is for the state to get out of the marriage business altogether, and simply to register domestic partnerships of various kinds for taxation and similar purposes. If people want to live in a menage a trois with people of the same or different sexes, they can register it with the state, and organise whatever religious or private ceremonies they regard as appropriate, without the state interfering in the definition of marriage, but simply noting the partnership for purposes such as tax or intestate inheritance.
These are just a few thoughts. I've been confused about the issue of marriage for a long time, and especially the involvement of church and state in marriage, Christians theologians don't seem to agree much about what it means. At one time the Greek government would not recognise a marriage between Greek citizens if it did not take place before a Greek Orthodox priest, yet in South Africa most Orthodox priests are not state marriage officers. The church just asks couples to bring along proof of state marriage registration. And from my experience the business of church ministers as state marriage officers is a racket, with marriage officers in some districts setting up cartels with price fixing and all the rest.
So at the moment I think that the state needs to give a great deal of thought to what exactly its concern with "marriage" is, and I really think that it is not for the state to determine what marriage is or isn't, but it does have a legitimate concern with the registration of domestic partnerships, but confining these to couples of different sexes or the same sex is really going off half-cocked. What about two unmarried sisters (or brothers, or brother and sister) who live together -- should they be excluded from registering a domestic partnership? And why should it be only two? The registration of such partnerships is a legitimate concern of the state, because of legal obligations and rights that can arise. Giving permission for surgery, for example, or regulating obligations under laws of contract. These things have nothing to do with "marriage".
And Christians need to give more thought to what exactly marriage is. People say that it is a question of equal rights, but equal rights to what?