It’d be a shame if there was a common condition in which people thought incorrectly that they were going to want to continue doing something for the rest of their lives, because once the condition passed they’d feel sheepish. It would however be quite a ripping practical joke to create an institution whereby people were given the opportunity to place legal and financial obstacles in the way of their stopping doing the thing their condition made them think they were going to always want to do. Presumably many people would take this offer, especially if there were tax advantages thrown in, and when the condition passed they'd be trapped! How we'd laugh at them. But enough about practical jokes: the rest of this post will be about marriage.
I’m not married, and I’ve never really come very close, but I’m only twenty-six and it wouldn’t surprise me if at some point in the next few years it becomes a live option. I’ve been thinking about it for some time now though, and I’ve been unable to come up with a satisfactorily large class of situations in which getting married would be rational.
It’d certainly make marriage rational if there was an all-powerful deity who would strike me down or at least damn me either to Hell or a long stint in Purgatory if I had sex with someone to whom I wasn’t married. If there was a deity like that then married sex really would be the only safe sex, and marriage would be sensible for those to whom celibacy doesn’t appeal. But I’m convinced there isn’t a deity like that.
The other obvious reason is if I expect her to want us to split up one day when I don’t want to. It’s harder to divorce a spouse than dump a merely significant other, and being married would raise the amount she’d have to want to be apart rather than together before splitting up was worth the trouble. Unfortunately for the cake and flower industries, however, I don’t have the preference distribution which rationalises this line of thought. Ceteris paribus, I want to be with people conditional both on my being in love with them and their wanting to be with me. So if they want to split up with me then I want this to be as easy as possible for them. I know I might not feel like that at the time, but I think that would be due to a failure of rationality on my part, and it’s foolish to take steps to indulge predicted failures of rationality. Odysseus knew when he heard the sirens he’d want to swim over to them, but since he knew this would be a failure of rationality he had himself tied to the mast so as not to act on his predicted irrational preference set.
A better reason to get married may be analogous to Odysseus’s reasons for tying himself to the mast: if you expect to irrationally want to split up with them at some point, then making this difficult for yourself is a good idea. I can see how that works, but it seems an extreme measure when in the event that you do irrationally split up you’ll have the option of getting back together once you’ve calmed down, as long as you don’t say things you can’t take back. A quick anger-management course seems more appropriate.
Asking around various wiser people than myself, the closest I’ve come to a satisfactory rationalisation is related but importantly different. If you both know it’s difficult for the other person to dump you, rationally or otherwise, then you can both relax. You don’t have to worry so much about how you look, saying the right thing, remembering birthdays etc. It’s tough keeping a relationship together, and without the obstacles to splitting up that marriage gives it’d be exhausting to keep it together for decades. The crucial thing is that you benefit from this ability to relax even if neither of you ever wants to split up. Now this kind of relationship presumably doesn’t appeal to everyone, and if it doesn’t then you probably shouldn’t get married. But I think it probably appeals to some people, and I wish them a long and happy life together.