Economics is the science of competing preferences, and if ever preferences have competed, they're competing in the Terri Schiavo case. So a little economic analysis might reveal an insight or two beyond what's already come out of this controversy.
First, whose preferences are we talking about? Terri Schiavo's? But Terri Schiavo has no preferences and hasn't had since the day when her consciousness was irretrievably lost. (There is, of course, some dispute about when this was, but I am accepting for the sake of argument that there's been no hope of recovery since long before the feeding tube came out.)
On the other hand, Terri Schiavo used to have preferences, and parties on all sides, who claim to know what those preferences were, have tried to invoke them. But why should we honor the preferences of someone who is no longer around to care what we do?
Sometimes we honor the preferences of the dead because we think the dead were unusually wise, or because "letting the dead decide" is a good rule for settling disputes without bloodshed; those are the reasons we look to the U.S. Constitution for guidance, but they don't seem particularly relevant here. The other reason to honor dead people's preferences—to enforce their wills, for example—is to alter their behavior before they die. If you promise me that my estate will go to my daughter instead of some random stranger, I'll work more and consume less—which means everyone else can afford to work less and consume more. (After all, everything I produce and don't consume is available for someone else—and available immediately, not just after I die.) That's a good reason to promise you'll enforce my will, and it's also a good reason to keep that promise, so people will believe such promises in the future.
On the other hand, I see far less reason why you should let me dictate, say, the disposal of my remains. I might have strong preferences about the matter, but once I'm gone, those preferences are quite irrelevant, and while I'm alive, your promise to enforce those preferences is unlikely to change my behavior in any socially useful way.
That's relevant to the Terri Schaivo case, because the same argument that applies to the disposal of a dead body applies as well to the disposition of a living but permanently unconscious one. Thomas Jefferson (one of those dead wise men who we sometimes go to for advice) admonished us that the Earth belongs to the living. Once Terri Schaivo essentially stopped living, it became frivolous to care about what she might prefer.
Now on to the preferences of her husband and parents. This is essentially a fight about what to do with her body: He wants to dispose of it; they want to feed it. And the question arises: Once someone has decided to dispose of a resource, why would we want to stop someone else from retrieving it? If I throw out a toaster, and you want to retrieve it from my trash, there's a net economic gain. If Michael Schiavo essentially throws out his wife's body and her parents want to retrieve it, it seems pointless to prevent them.
Except for the fact that Michael Schiavo wants to prevent them, and economic analysis tends to presume that all human wants should be respected. Except that I wonder about that.
One of the great joys of being a libertarian economist is that libertarianism and economic analysis are so frequently in harmony—as a general rule, freedom tends to promote the fulfillment of human desires. But not always. Suppose there is a segment of the population who wants to censor, oh, say, the radical thought of William Saletan. Many of us get a lot of pleasure from reading Saletan, but the anti-Saletanians would get (let us suppose) far more pleasure from banning him. Once we've agreed on an appropriate way to measure that pleasure, a strict cost-benefit analysis might argue for a ban from which a libertarian would recoil.
The solution to this, it seems to me, must be to say that certain preferences shouldn't count when we do cost-benefit analysis. In particular, a preference to prevent someone else from doing something he wants to do, just for the sake of stopping him, is not a preference we want to cater to. That's a very dangerous position, because it raises all sorts of questions about where to draw the line, and I have no idea how to answer most of those questions. (For example: How do we distinguish between "I don't like you reading Saletan because I think it's dangerous" and "I don't want you reading Saletan because I just don't like it"? And does the difference matter?) But the alternative, it seems to me, is to endorse the tyranny of the bluenoses.