So Tygr and I, having analyzed the growth potential of Raleigh, have hypothetically decided that land near where he lives is going to become very valuable in ten years or so, and buy up a 100-acre tract “out in the slashin’s” with the intention of splitting the property taxes on it for ten years and then selling it, hopefully at a killing. But one or both of us may not live out that ten years, or one of us may need to sell off his share because he needs the money. We could, of course, write a detailed deed in which what happens in any of fifty possible scenarios is spelled out.
But we don’t need to – all we need do is say that we hold the land as tenants in common, and state law covers all 50 scenarios. If we jointly disagree with the default position for tenants in common and want to write in that, say, in the event of his death or incapacity the land will go to Jkayla and not to the Tygr Cub, who at two is not suited to manage land by herself and having a share of his interest in trust for her would unnecessarily complicate the situation, we can do so – but the default positions are already spelled out for us, so we don’t need to analyze all of them.
It’s in an analogy to that basic concept that legal marriage has its proper place. It’s in society’s interest to ensure that minor children are provided for by their parents rather than the taxpayers, to the extent possible, and that persons (usually the mothers, but not always) whose careers have been interrupted by the need to bear and raise those children have economic assets. And that there are options in place in law to provide for unforeseen circumstances that do occur in people’s lives.
The legal conception of marriage is that it provides those default options as a matter of standard law. They can be superseded by agreements between the parties to the marriage, to be sure. And dissolution of a marriage with children is not as simple as dissolution of a partnership. (Going back to the land-investment partnership analogy, think of it as Tygr and I having decided to plant a grove of trees which will take 20 years to produce a viable crop but which need constant tending until then. If we fall at odds over the property, who’s going to ensure those trees are taken care of?)
Now, I would have no problem with two gay people marrying, and (aside from personal moral convictions that I do not believe I have any right to enforce on others) I would have no problem with a hypothetical polyamorous multi-person marriage. But these are not arguments against legal marriage; they’re arguments for allowing an expanded definition. If you personally feel it’s immoral to marry another man (or another woman, if you’re female) or a group of other people, then don’t. But don’t try to enforce your definition of what’s a morally valid marriage on others who disagree with you.