Why should we respect the wishes of the dead?

Having become overloaded by commentary on Terri Schiavo in the past week, I'm reluctant to add to the whole mess. Still, I had one thought of a more philosophical nature spurred by PZ Myers and Abiola Lapite. Both of them expressed the view that, since Terri has no higher brain function and has no idea whether her pre-vegetative wishes for medical treatment are being adhered to or not, we need not consider her wishes. That is, she has no dignity left to preserve, since she is unaware of her surroundings, so there's no real reason to go either way.

This brings up a thought experiment I have heard a few times. Suppose I offered you $10, in exchange for which a room full of people far away from you would insult you behind your back, call you ugly, stupid, mean, and so on. That doesn't sound very appealing - generally we desire people not to insult us, even if these insults have no effect on us (e.g., it's not the case that these backstabbing insults cause anyone to treat you worse than they otherwise would have). But suppose I offered you $10, in exchange for which people would insult you but I would then erase your memory of our agreement, and you would believe I had just been very generous in giving you $10. That doesn't sound very appealing either. Most people's intuition is that they want their desires to be fulfilled even if they don't know about it.

This is similar to people's wishes about what happens after they die. People care about what kind of funeral they have, whether they get cremated or buried in a coffin, and so on. People usually don't want their corpses to be desecrated. People care about whether they are remembered well or poorly. And people care about abstract ideals like whether democracy will survive in the world, whether global warming will ruin the planet. This is the sentiment of "I can die happy now that I have accomplished long-lasting achievement X," or in the negative, "X must be turning in his grave now that his ideals have been betrayed."

Still, we're left with the question of why we should care about these wishes. There is no person who gets concretely harmed if someone's wishes are contravened after their death, or unbeknownst to them. "What you don't know can't hurt you," etc. Yet it still feels wrong. It feels like betrayal. Why?

One practical argument is that living people want to have confidence that their wishes will be obeyed. Every betrayal of a dead or unconscious person's wishes is a blow to that confidence, and thus harms (in a small way) almost all living people.

Yet that doesn't seem quite right either. Wish-betrayal also seems wrong even if you do it secretly such that no one else ever finds out. Moreover, my intuition is that wish-betrayal is bad relative to a specific person (i.e., the person whose wishes you're betraying), not just humanity in general. But how can this be, if that person never finds out that you have betrayed his or her wishes?

Let's try another tack: There is a badness to dying that is completely independent of whether you suffer - it is the ultimate harm, even though "you" are not really being harmed at all, if you don't suffer. Death seems to be bad because it causes us to lose all the life experience we might otherwise have lived. You lose your opportunity to fulfill your goals and desires, whatever they may be. So if those who survive you continue to fulfill your goals and desires, that makes it slightly less bad. This is so even though you are unaware of what actually happens - our intuition suggests that the goodness of fulfilling your desires and the badness of having them frustrated doesn't depend on you knowing about it.

Still, I'm stuck on the problem of the fact that after death, you no longer exist - there is no subject to relate to the fulfillment or frustrations of your pre-death desires. Could it be that intuition in this case is hopelessly confused? It wouldn't be the first time, after all. It may be that this intuition just arises from the desperate hope (even among atheists) that life continues in some form after death, and that preserving a dead person's wishes is just a way of assuring ourselves that the dead person still lives on in our hearts.

Thoughts, anyone?