Marriage: What and Why?

As promised, here's Topical Post #2 for today. This topic is much more confusing for me. Where I was fairly confident in my opinions with the last post, this time I'm seriously confused. This is more of a "thought experiment" than an argument per se, and I would very much appreciate comments and discussion on this topic.

So yesterday the New Jersey Supreme Court opened up the door for even more debate about the issue of gay marriage. According to an MSNBC article, the court said that the NJ legistlature "must offer homosexuals either marriage or something like it, such as civil unions."

As such things will, this got me thinking. What is the difference between a "marriage" and a "civil union"? For that matter, what exactly is marriage? The following are my thoughts on the subject, but they are far from complete. I need input from others, particularly if you know something about marriage laws and benefits (more on that later). In a nutshell, I'm trying to answer these two questions:

Why should we have marriages? What is the purpose of marriage?

First, let me offer a basic definition of "marriage": Marriage is a union between individuals in which the participants ("partners") devote themselves to one another for life. That's a rather broad (and therefore somewhat vague) definition, but I think it has to be for the discussion to continue.

On the face of it, it looks pretty simple: an agreement between individuals. Which leaves me wondering: "Why should an outside entity (church, State, the Mob, etc.) have anything to do with such a personal matter?"

Let's get the Christian answer out of the way: Marriage was established by God for a variety of reasons. Christians get married because God said they should (under certain circumstances; Cf. 1 Corinthians 7), and they follow His rules about how to go about it. Other religions have similar guidelines for marriage.

For the remainder of this post (and in all discussion that follows), I'd like to focus on secular (non-religious) marriage. Why exactly does/should the secular world have marriage at all? Why have the State oversee and legalize marriage? Why provide benefits to married couples? (This is where I could really use some help; I know basically nothing about the tangible/State-given benefits that marriage provides. Any information to that effect would be appreciated.)

Reason One: Children
I think the number-one reason for secular marriage is to provide for children. If one hears much at all in the marriage debate, one is likely to hear a great deal about "The Family." "Marriage is the foundation of the Family, and the Family is the foundation of society," it might be said. How is this so? I think it primarily has to do with raising children. Children, an old cliche tells us, are the future. As such, the State has a vested interest in the well-being of the children that live under its influence. This explains why married couples receive benefits of a variety of kinds.

If secular marriage is about raising children, then it should be easy to decide who gets to marry: Any union that benefits children is a good one. If a heterosexual couple can raise a child better than a single parent, let them marry. If a homosexual couple can raise a child as well as a heterosexual one, let them marry. If a single man with a dog provides the same developmental benefits to a child, let man and dog be wed (with appropriate benefits to the man). If it truly does take a village to raise a child properly, polygamy must return.

Of course, the process for evaluating which possible arrangements are beneficial to children is neither easy nor quick. So, until all possibilities have been examined, it seems (from an economical perspective) that the secular insitution of marriage must be either exclusive (some arrangements get benefits while others don't) or nonexistent (nobody gets married).

Reason Two: Validation
Some might suggest that having a relationship "sanctioned" by an authoritative body makes the relationship better. Perhaps it helps hold the partners accountable to their vows. Perhaps it gives the partners a sense of pride (or even superiority) to know that they have the blessings of the State. I suppose there could be any number of such reasons.

If secular marriage is about providing validity to a relationship, then why isn't it available to other relationships: parents and children, siblings, close friends, employers and employees, teachers and students, roommates? What is it about one kind of relationship that makes it more fit for the State's acknowledgement and blessing? Is it physical intimacy? The amount of time spent together? Common interests? Psychological compatibility? The only worthwhile reason I can think of is the raising of children, which has already been discussed.

Reason Three: Social Stabilization
It has been suggested that marriage acts as a stabilizing factor in society. I don't know enough about such arguments to deal much with them here, but I will make a few comments. Just because marriage correlates to stabilization doesn't necessarily mean that it is a cause of stabilization. To put it another way: Is the stabilization caused by the institution of marriage or by the commitment-relationship of the married? If most married couples are religious (I suspect not, but it could be), then perhaps religion is the stabilizing factor. Or maybe it's parenthood and children. My point here is that marriage is a rather complex (and somewhat vague) process/lifestyle, and the bureaucratic "institution" of marriage may play a smaller role in any benefits of marriage than we would like.

Regarding "Benefits"
I've already said that I'm not really familiar with how marriage benefits work, but there is a particular aspect of them that I'm curious about: Are marriage benefits a reward or an assistance? This is related to the purpose of marriage: If marriage is meant for the betterment of children, then marriage benefits are more likely a form of aid to the parents, to help them raise the children. On the other hand, if marriage is instituted for the betterment of society at large, then marriage benefits seem more like a reward or an incentive to encourage people to marry.

If marriage benefits are primarily a reward, I wonder if that could actually be harmful to society. If people get married just for the benefits, the marriage itself could be less stable, and I suspect that divorce undoes most or all of the stabilizing benefits of marriage.

Concluding Thoughts
The long and short of all that musing is this: It seems to me that the marriage debate is all wrong. Politicians spend lots of time arguing about the details of how marriage should work without addressing why it exists in the first place. I see only two good reasons even to have an institution of marriage. The first is for the sake of religion, in which case the State has no business getting involved. The second has to do with raising children, and I outlined by thoughts about how such marriage should work in section one above (exclusivity or nonexistence). I freely admit that there are probably reasons for secular marriage that I haven't thought of, and I hope that readers who know some will share them. But for now, I'm starting to think that secular marriage shouldn't exist.

As a reminder for would-be commenters, I'm basically trying to address these questions:
Why should the State have marriages? What is the purpose of secular marriage?