There are various objections to expanding the conventional, up-tight, as-God-intended "one man, one woman" notion of marriage but by far the least plainly bigoted ones I am aware of are the bureaucratic ones.
To be blunt, the systems aren't set up to handle it. The paper forms have a space for the husband's name and a space for the wife's name. Married people carefully enter their details in block capitals and post the forms off to depressed paper-pushers who then type that information into software front-ends whose forms are laid out and named in precisely the same fashion. And then they hit "submit" and the information is filed away electronically in databases which simply keel over or belch integrity errors when presented with something so profound as a man and another man who love each other enough to want to file joint tax returns.
This is a playful take on the technical side. I'm told it's in SQL, but it's somewhat enjoyable even if you skim the technical details. Or at least if this is the sort of thing you like, there's plenty of it.
The real world has a much wider bandwidth than anything which can be expressed by characters in a row. In particular, its assumed that everything takes place in a jurisdiction with only definition of marriage, and as is pointed out in the comments, polygamy isn't covered adequately. I'm guessing that the author is youngish-- the assumption is that divorce or annulment are the only ways for a marriage to end.
Still it's a clue for those of us who need it that even fairly simple situations need to be thought about carefully if they're to be put in databases.
Link thanks to siderea.