One of the craziest things I discovered when I was first learning French was that the French have laws about what you can and can't name your kids. They've relaxed the laws a bit in the past few years, but it used to be that you had to choose the given names from a big list (of Catholic saints) and the kid's last name was determined by a simple algorithm: it's the same as the last name of whichever parent gets to city hall first to declare the baby's birth. (The dad has a bit of an advantage here, not being stuck in a hospital bed.) Or, if the parents are legally married, then the kid would get the father's last name.
Also, under normal circumstances you can't change your own name at all. I think they grant a special exception if your last name is "La Merde" or something, but I'm not certain. Actually, there is one exception: If you're a woman and you get married, then you weren't allowed to not change your name.
This whole idea took me completely by surprise. How could it be the state's business to choose what you can and can't be called? I understand that there are legal reasons to keep track of people's identities (for example, I think in the U.S. if you want to change your name you typically have to declare that it's not for the purpose of hiding from creditors or the law). But it seems like it should be the individual's (or family's) job to select the name, and the government's job to just make a note of it.
I was thinking about this the other day with respect to gay marriage.
The thing is that the marriage-type relationship exists in every human society. If you go to another country, you'll meet plenty of couples that you perceive as "married" -- even if in their country they use a different word, and even if their country's legal documentation for marriage is totally unfamiliar or non-existent. Sure, the corresponding rights and responsibilities vary from one culture to the next just as the behavior of parents towards their children varies from one culture to the next. But the relationship itself -- to be someone's spouse -- you understand it as intuitively as you understand what it means to be someone's brother or someone's mother.
Legal identity documents (for birth, adoption, marriage, death, etc.) can have some effect people's perceptions and behavior. For example, if a French person doesn't like being named after a Catholic saint and decides to ask all his friends and colleagues to call him "Rainbow Appleseed" or something, he'll discover this is a huge pain in the butt to explain every time he has to fill out any forms (a surprisingly frequent occurrence in France). I learned this lesson myself, actually. As a young, idealistic American feminist, I decided that I wanted to keep my own name rather than taking my husband's (because your name is your identity!) But after less than a year in France, my laziness won out over my principles and I took to just introducing myself as "Madame husband's name" in all situations except my own work. Legally I never did change my name, but French forms -- instead of having one "last name" slot -- have separate lines for "maiden name" and "husband's name". So I fill out these lines accurately and Voila ! -- the fact that my husband's name doesn't appear on my U.S. passport becomes a minor technicality...
But what is in a name? A rose by any other name would smell as sweet.
I think that people who say "the solution is for the government to get out of marriage altogether" are missing the boat. The underlying kinship relationships exist whether the government writes them down or not, and a society that needs legal identity/kinship documents such as birth, death, and adoption certificates has an interest in correctly documenting marriages as well. There are a number of rights and responsibilities that follow from kinship relationships (inheritance, immigration, next of kin, etc.), and "spouse" is a kinship relation that is as fundamental as "parent" or "sibling."
Similarly, those who think they can keep couples from being married -- just by denying them the word "marriage" or the legal recognition for it -- are deluding themselves. Sure, you can make life inconvenient for some couples by making them go back to doing it the old-fashioned way: by declaring their commitment in front of witnesses (without the corresponding legal identity papers).
And it's true that by restricting marriage documents (in a society that normally uses them), one can create a host of minor-to-major problems for the families that aren't legally documented. But it won't change the underlying reality of which couples are married according to the common perception of what it means to be married. It's just a question of cleaning up the paperwork.
see also Discrimination against homosexuals: why? why? why??? and Why? Why? Why??? II