The fact that someone would be willing to forgo a decent diet in order to build a monument to his god does not mean that his claim on others for aid in his project has the same strength as a claim for aid in obtaining enough to eat. (Scanlon 1975)
Consider next Desire-Fulfilment Theories. The simplest is the Unrestricted Theory. This claims that what is best for someone is what would best fulfil all of his desires, throughout his life. Suppose that I meet a stranger who has what is believed to be a fatal disease. My sympathy is aroused, and I strongly want this stranger to be cured. Much later, when I have forgotten our meeting, the stranger is cured. On the Unrestricted Desire-Fulfilment Theory, this event is good for me, and makes my life go better. This is not plausible. We should reject this theory. (Parfit 1984)
If I have a bad headache, anyone has a reason to want it to stop. But if I badly want to climb to the top of Mount Kilimanjaro, not everyone has a reason to want me to succeed. I have a reason to try to get to the top, and it may be much stronger than my reason for wanting a headache to go away, but other people have very little reason, if any, to care whether I climb the mountain or not. Or suppose I want to become a pianist. Then I have a reason to practice, but other people have little or no reason to care if I practice or not. (Nagel 1986)
For example many Boston residents desperately wanted the Red Sox to win the World Series in 2004. Their happiness when the Red Sox won gave others – even Yankees fans – some reason to judge it to be good for them that their preferences were satisfied. But, as Nagel maintains, the mere preferences of Red Sox fans, as opposed to their happiness or unhappiness, is of no moral importance to others. (Hausman 2012)
As someone more sympathetic to preference-based views than the alternatives, I don't find any of these arguments persuasive, although Parfit's is closest. The others all seem pretty paternalistic. If something matters to you, shouldn't it matter to me in my concern for your interests?
In Parfit's case, my response would just be that it doesn't matter for their welfare because the preference is not held by them anymore, or if it is still held, why should it be the case that only things that affect our experiences matter? I think Parfit is just asserting this is implausible, with no further argument.
Another example might be people doing things to your body without your consent while you're unconscious in a way you never find out. I think the best explanation for why this is wrong is simply that you prefer this not happen, whether or not you find out, and regardless of indirect effects. If someone feels violated after finding out, I think you'd have to claim that this is an irrational reaction and that informing someone they've been touched without their consent is what causes them harm, not the actual nonconsensual act. If someone would prefer to know about something they know they'd feel bad to find out, isn't it still right to tell them?
Also, this gets into the experience machine thought experiment. See https://forum.effectivealtruism.org/posts/vWqMzv97ueX8iagg8/contact-with-reality
Us not wanting people to do things with our body without our knowledge is indeed a different argument, one which seems to show that at least some preferences matter ethically. But preference utilitarianism is usually the view that only preferences matter, perhaps even all preferences.
Regarding Parfit's case, is this not the same as me being unconscious while my body is manipulated? In both cases we do not seem to currently hold a preference. In one because he forgot about it, in the other because I'm unconscious.
But even suppose Parfit did not forget about the stranger. Why would it be good for Parfit that the stranger is cured, without his knowledge? To me it does not seem to be good for him. And wouldn't such a view have the unfair consequence that it is much less important to cure a lonely person about whom no other people care than a popular person about whom lots of people care, even if those are not informed about the cured illness?
I don't think it's necessarily true that you hold no preferences while you are unconscious (and not dreaming), which seems to be what you're suggesting. The preferences are still probably encoded in your brain somewhere, either explicitly, or as a general response tendency.
"And wouldn't such a view have the unfair consequence that it is much less important to cure a lonely person about whom no other people care than a popular person about whom lots of people care, even if those are not informed about the cured illness?"
Is it more unfair because they aren't informed? I think it's already unfair if they are informed. I think this only seems worse if you assume the conclusion that if you never find out, it shouldn't matter.
To be clear, though, I think it's very plausible preferences matter more if you're informed about their extent of satisfaction, because the experience of satisfaction or frustration matters, too.
Yeah, preferences may still be latent dispositions in case of unconsciousness, but the same seems plausible for Parfit's forgotten stranger. If he is reminded of them, his preference may come back. So the two cases don't seem very different.
Well, it is presumably less unfair if they are informed, because it would make them happy to learn that the person is cured, which matters, at least somewhat. And yes, my (and Parfit's) intuition is that if they never find out that the person was cured, this would not be good for the carers. So curing the cared-about person would not be better than curing the person about whom no one else cares. That's not a conclusion, it's a more a premiss for those who share this intuition.