Marriage is a Social Construct

I recently read this article opposing same-sex marriage. It's probably the best article I've seen opposing it but it's still wrong. Here's why:
There's a decent critique here.

But more importantly, the article depends on the reader's instinct to agree with them. I think that the key to understanding their persuasiveness is seeing the way they try to force the reader to agree that marriage is some sort of "natural kind" that has a real essence about which we can be right or wrong, as opposed to a social construct, which is just whatever we make it. The authors try to discourage people whose instinct is to support same-sex marriage from taking the constructivist line by saying that for marriage to be a right, it has to be a real thing with an essence.

Even if marriage did not have this independent reality, our other arguments against revisionists would weigh equally against constructivists who favor legally recognizing same‐sex unions: They would have no grounds at all for arguing that our view in‐ fringes same‐sex couplesʹ natural and inviolable right to marriage, nor for denying recognition to unions apparently just as socially valuable as same‐sex ones, for marriage would be a mere fiction designed to efficiently promote social utility.

It certainly seems that asserting the constructivist line would preclude rights-talk. I'm not sure if they're doing this deliberately or not but it seems that this line works by making the reader think that the social constructivist line precludes all moral assessment of the situation, not just rights-based ethics. If we think fairness is a virtue, same-sex marriage is in, even if it is a social construct.

The authors do have another follow-up argument, which happens to take a consequentialist line. They claim that monogamous heterosexual marriage is the only sort that will lead to maximal societal harmony and that anything else would actively erode the current situation. It would make me very uncomfortable to say that we should employ a useful fiction à la Plato's Republic but, if they had decent empirical data to support it, they'd have half an argument. But they don't really.

I have to say, though, that I'm grateful to the authors of this paper for helping me bite the bullet and realise that marriage really is a social construct. It's clear that polygamous and incestuous unions are not marriages in contemporary western society but who would say that Hussein bin Ali really was married to his first wife but nos 2-4 were mere concubines? Who would say that Cleopatra wasn't really married to her brothers, Ptolemy XIII & XIV even when their being married was crucial to their position in Macedonian Egypt? There might be plenty of moral arguments against polygamy and incest but that doesn't mean it can't be called marriage.