I've talked before about consequentialism, but at the time I put to the side what consequences one should be striving for. It's no small consideration: not only will a person make very different moral choices based on what consequences they are aiming for, but choosing the wrong consequences can seem to refute consequentialism altogether.
I mean, consider the basic utilitarian formulation: "the greatest happiness for the greatest number." In that case ought we to euthanize unhappy people, to increase the sum of happiness in the people who are left? If we get the technology to put wires in people's heads that make them feel happy all the time without changing any of the realities of their lives (say, they are still hungry and filthy and sick, but they just don't mind anymore), should we impose that on everyone?
That's where preference utilitarianism comes in -- rather than say "the goal is to make everyone happy," we could say, "the goal is to give everyone, so much as possible, what they want out of life." So we shouldn't wirehead people unless that's truly what they want. But that raises more problems: does that mean that, rather than taking a suicidal person to the hospital, we should give them a big bottle of sleeping pills because that's what they want? Yet, of course, the second we edit it to "what a person of sound mind would want" or "what a well-informed person would want" we run the risk of invalidating everyone's preferences because, after all, that isn't what they really would want if only they were as mentally healthy or well informed as us.
Existence is the third possibility. Rather than preserve happiness even at the cost of ending some people's existence, we should preserve life above all. I'm a fan of this, for sure. After all, when considering whether a public-health proposal is a good one, we ask not "will people like it?" but "how many lives will it save?" If saving lives is one's end goal, it seems like it wouldn't wind up with anything really monstrous. Except .... well, we don't actually force medical interventions on people, even if they're really helpful ones. Take the extreme case: a very elderly person, someone who has a short time to live in any case, and who has begged not to be rescucitated again and again, but to die naturally? Is it right to overrule their preference because preserving life trumps everything else?
Another consideration is how we are to rate existence for those who do not yet exist. Is it morally equivalent to save a life and to bring a new life into existence? Well, not really -- a person who currently exists has rights, responsibilities, preferences, loved ones, and so on, while a person who doesn't isn't tied into the present reality in any way. To choose not to beget them is no injustice to them, because they don't exist. But if we really were taking existence alone as the only consequence of importance, we would consider saving a life equal to creating a life, because both result in an equal amount of existence. I do think creating a life has value -- that is part of why I've done it so many times! Sociologists may remind us that becoming a parent is likely to reduce our happiness (and I think they're right, in at least one sense) but that doesn't really matter all that much to most people. On the one hand, we have preferences beyond happiness, and on the other, the child you have will have infinitely increased happiness once they exist. But I feel odd about saying, "I'm having this child because he will increase the sum of happiness in the world." I'd rather simply say, "I'm having this child because it is a good thing for him to exist."
In the end, my choice has been to balance all three of these considerations: existence, preference, and happiness -- which could also be stated, "life, liberty, and happiness." To pursue any one of these completely without reference to the other two has the potential to be drawn out to morally repellant conclusions. I think in most cases that doesn't even come up because the three are interconnected. You can't be happy if you are dead; most people prefer to be alive; most people are made unhappy by not being free to pursue their wishes. But in case it should come up, I think it's appropriate to balance them. If, for instance, a person desires to die, one might simply overrule that because life has value apart from your preference, and because the person has an opportunity they don't recognize for future happiness. And yet, when my grandmother chose to forego cancer treatment, her wish was respected because it was a clear, sane, adamant preference being weighed against a very short increase in lifespan anyway. I can save the threatened suicide victim but not kidnap my grandmother to force treatment on her, without being a hypocrite, because I see in one case a weak preference (because it may be compromised by poor mental health) weighed against a great deal of potential life and happiness, while in the other I see a strong preference weighed against very little life and no increase in happiness (because death would have been slower and more painful).
How much weight ought to be put on each one? It's not really possible to say. I tend to rate life the most highly; I think each person is an irreplaceable individual with much to offer the world, so that even if they do not seem very happy, they still have value. I know others who care more about liberty -- they were not exaggerating when they said, "Give me liberty or give me death!" Many have died rather than endure what they perceived as slavery. And some people care more about happiness; they feel their life is better spent bringing joy to others' lives than curing diseases. I don't think any of these weightings is wrong, though I do think it would be wrong to consider only one while entirely neglecting the others. To pursue a course of action which serves one of these ends while destroying another -- for instance, wiping out life on earth because people aren't happy enough, or having twenty children and neglecting them all because at least they would exist, or wireheading everyone against their will because it would make them happier -- would be a morally repugnant thing to do.