This article is a stub. Alas, you can't help Wikipedia (or LessWrong) by expanding it. Except through good comments.
Here I'll present an old idea for a theory of population ethics. This post exists mainly so that I can have something to point to when I need this example.
Given a total population , each with total individual utility over the whole of their lives, order them from lowest utility to the highest so that implies . These utilities are assumed to have a natural zero point (the "life worth living" standard, or similar).
Then pick some discount factor , and define the total utility of the world with population (which is the total population of the world across all time) as
- .
This is a prioritarian utility that gives greater weight to those least well off. It is not average utilitarianism, and would advocate creating a human with utility larger than than all other humans (as long as it was positive), and would advocate against creating a human with negative utility (for a utility in between, it depends on the details). In the limit , it's total utilitarianism. Increasing someone's individual utility always improves the score. It (sometimes) accepts the "sadistic conclusion", but I've argued that that conclusion is misnamed (the conclusion is a choice between two negative outcomes, meaning that calling it "sadistic" is a poor choice - the preferred outcome is not a good one, just a less bad one). Killing people won't help, unless they will have future lifetime utility that is negative (as everyone that ever lived is included in the sum). Note that this sets up a minor asymmetry between not-creating people and killing them.
Do I endorse this? No; I think a genuine population ethics will be more complicated, and needs a greater asymmetry between life and death. But it's good enough for an example in many situations that come up.
It's been a long time since you posted this, but if you see my comment, I'd be curious about what some others patches one could apply are. I have pretty severe scrupulosity issues around population ethics and often have trouble functioning because I can't stop thinking about them. I dislike pure total utilitarianism, but I have trouble rejecting it precisely because of "galaxy far far away" type issues. I spend a lot of time worrying about the idea that I am forced to choose between two alternatives:
1) That (to paraphrase what you said in your critique of total utilitarianism) it is a morally neutral act to kill someone if you replace them with someone whose lifetime utility is equal to the first person's remaining lifetime utility (and on a larger scale, the Repugnant Conclusion), or
2.That the human race might be obligated to go extinct if it turns out there is some utopia in some other branch of the multiverse, or the Andromeda Galaxy, or in some ancient, undiscovered fallen civilization in the past. Or that if the Earth was going to explode and I could press a button to save it, but it would result in future generations living slightly lower quality lives than present generations, I shouldn't push the button.
I'd really like to know some ways that I can reject both 1 and 2. I really admire your work on population ethics and find that your thinking on the subject is really closely aligned with my own, except that you're better at it than me :)