Perhaps there is more of importance than merely welfare. Concerning the repugnant sadistic conclusion I can say two things. First, I am not willing to put myself and all my friends in extreme misery merely for the extra existence of quadrillions of people who have nothing but a small positive experience of tasting an apple. Second, when I would be one of those extra people living for a minute and tasting an apple, knowing that my existence involved the extreme suffering of billions of people who could otherwise have been very happy, I would rather not exist. That means even if my welfare of briefly tasting the apple (a nice juicy Pink Lady) is positive, I still have a preference for the other situation where I don’t exist, so my preference (relative utility) in the situation where I exist is negative. So in the second situation where the extra people exist, if I’m one of the suffering people or one of the extra, apple-eating people, in both cases I have a negative preference for that situation. Or stated differently: in the first situation where only the billion happy people exist, no-one can complain (the non-existing people are not able to complain against their non-existence and against their forgone happiness of tasting an apple). In the second situation, where those billion people are in extreme misery, they could complain. The axiom that we should minimize the sum of complaints is as reasonable as the axiom that we should maximize the sum of welfare.
I have a paper about complaints-based theories that may be of interest—https://www.journals.uchicago.edu/doi/abs/10.1086/684707
One argument I advance there is that these theories appear not to be applicable to moral patients who lack rational agency. Suppose that mice have net positive lives. What would it mean to say of them that they have a preference for not putting millions in extreme misery for the sake of their small net positive welfare? If you say that we should nevertheless not put millions in extreme misery for the sake of quadrillions of mice, then it looks like you are appealing to something other than a complaints-based theory to justify your anti-aggregative conclusion. So, the complaints-based theory isn’t doing any work in the argument.
Thanks for the paper!
Concerning the moral patients and mice: they indeed lack a capability to determine their reference values (critical levels) and express their utility functions (perhaps we can derive them from their revealed preferences). So actually this means those mice do not have a preference for a critical level or for a population ethical theory. They don’t have a preference for total utilitarianism or negative utilitarianism or whatever. That could mean that we can choose for them a critical level and hence the population ethical implications, and those mice cannot complain against our choices if they are indifferent. If we strongly want total utilitarianism and hence a zero critical level, fine, then we can say that those mice also have a zero critical level. But if we want to avoid the sadistic repugnant conclusion in the example with the mice, fine, then we can set the critical levels of those mice higher, such that we choose the situation where those quadrillions of mice don’t exist. Even the mice who do exist cannot complain against our choice for the non-existence of those extra quadrillion mice, because they are indifferent about our choice.