The excellent blogger Welmer cogently reviews the purpose of marriage:
First, in all likelihood, to keep the peace. In the animal kingdom, ritualized violence is often an important aspect of sexual competition. Humans, however, are equipped with a far more deadly weapon — reason. The lower mammals may fight hard for female attention, but some genetic imperative prevents them from killing each other, whereas humans (as well as chimps — our closest cousins) discovered that murder is far more conclusive in settling the matter of which male gets the prize. Indeed, women have been taken as booty from the earliest days of tribal skirmishes with spears and clubs.
Old fashioned murder was not particularly different from the modern sort. It was often a group effort, which we know as “war.” Warfare over females is common in hunter gatherer societies, and serves as a check on population growth not only due to the murder of men but the associated killing of their children. Even the most primitive tribesmen must have known that when a man is deprived of female companionship, he becomes inclined to take a female by any practical means. Men with female sexual partners must have felt rather nervous about this, and so developed pacts with other men to protect their status with their women. Thus the concept of marriage developed as a mutual recognition between men of the legitimacy of the male/female reproductive partnership. As long as this recognition existed within a given tribe, peace would be easier to preserve, and both men and children were safer than otherwise.
However, guarantees within a tribe didn’t generally apply to outsiders, and raids for women characterize primitive societies both past and present. The easiest tribes to raid were certainly those that had no concept of marriage, because the males would not be inclined to defend other men who had no respect for their own status with women. Repeated over time, this guaranteed the eclipse of tribes without a clear concept of marriage by those that did.
He also summarizes the problems facing marriage:
Although the government still preserves some legal relics of the previous norm, including the recognition of marriage and certain tax categories, it is an undeniable fact that the family has taken a subordinate role in regards to the desires - however transient - of the individual. No fault divorce, decriminalization of adultery and skyrocketing illegitimacy rates bear this out. The law has changed to reflect the new state of affairs, treating marriage and its dissolution as economic transactions while ignoring the effects they have on social stability. This is justified on the dictate that individual freedoms and rights trump, or are in the interest of, the greater good. This may be true or false. There is no doubt that some highly collectivist societies (such as North Korea) can turn out very badly by a number of measures, but the philosophy of extreme individualism often masks collective efforts by one group to gain leverage over another.
And then . . . he throws it all away!
Whether the West’s extreme individualism is good or bad on the balance is of little concern in an effort to revive an institution that is on life support and in danger of catastrophic failure — there simply isn’t enough time to reevalute our civilization’s shibboleths to revive marriage as it was. Rather, we must work with what we have, which is a strong focus on civil rights and freedoms. From that perspective, it can be argued that the traditional concept of marriage is a fundamentally unjust institution that privileges some people at the expense of others, and in fact unreasonably restricts the rights of those who enter into it. Therefore, the abolition of marriage must be considered to achieve a greater degree of freedom and justice in society. States may retain civil partnerships entered into under contractual agreements, but these must be little different from corporations or partnerships entered into for business purposes.
Would that marriage was "little different from corporations or partnerships entered into for buisness purposes"; these, at least, cannot be unilaterally dissolved, but as in any contract they "restrict the rights of those who enter into it," unreasonably or no. I don't really have a problem with thinking of marriage as a sacralized contract, but Welmer, at least here, seems not to understand that contracts, while voluntarily entered, bind the parties to certain future courses of action. And if the marriage contract means anything, then sexual exclusivity is the fundamental provision of that contract.
More generally, while Welmer correctly apprehends the manner in which communally enforced marital rights and obligations enabled social cooperation, especially among men, he doesn't address the dynamic of conquest that made such cooperation necessary. Does he think that such cooperation is no longer necessary? What happens when we have a conflict with a people who have not discarded it? Sure, we have our technology, but what of the political will to use it? And what of our own internal divisions?
To be fair, Welmer appreciates the importance of monogamy, and specifically denies the intent to discard it. But can it survive legal protection? Roissy is on his blogroll, so I would think he understands what the weakened state of monogamy looks like. I don't see that state improving by abolishing what remains of its legal status.