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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.
I have realized that I am coming off like I don't understand algebra, which is a result of my failure to communicate. As unlikely as I am making it sound, I understand what you are saying and already knew it.
What I mean is this:
Despite a = b, it could "look like" a < b or b > a if you didn't have access to the world but only to the (expanded) sum. If you can ask for the difference between the total sum and the sum ignoring a, but not for the actual value of a.
I can't think of a non-pathological case where this would actually matter, but it seems like a desirable desideratum that a = b will always "look like" a = b regardless of what kind of (sufficiently fine-grained) information that you have.
EDIT : After reading your above comment about willingness to sacrifice elegance, I kind of wish I hadn't said anything at all, considering my comments are all in the interest of what I would consider elegance. To be sure, I think elegance is a legitimate practical concern, but I wouldn't have engaged with you initially had I known your view.