I don’t see why the A-Z comparison is unreliable, based on your example. Why would the intuitions behind the repugnant conclusion be less reliable than intuitions behind our choice for some axioms? And we’re not merely talking about the repugnant conclusion, but about the sadistic repugnant conclusion, which is intuitivelly more repugnant. So suppose we have to choose between two situations. In the first situation, there is only one next future human generation after us (let’s say a few billion people), all with very long and extremely happy lives. In the second situation, there are quadrillions of future human generations, with billions of people, but they only live for 1 minute where they can experience the joy of taking a bite from an apple. Except for the first generation who will extremely suffer for many years. So in order to have many future generations, the first of those future generations will have to live lives of extreme misery. And all the other future lives are nothing more than tasting an apple. Can the joy of quadrillions of people tasting an apple trump the extreme misery of billions of people for many years?
On the critical level theory, the lives of the people who come into the world experiencing the joy of an apple for 1 minute have negative value. This seems clearly wrong, which illustrates my point. You would have to say that the world was made worse by the existence of a being who lived for one minute, enjoyed their apple, then died (and there were no instrumental costs to their life). This is extremely peculiar, from a welfarist perspective. Welfarists should be positive about additional welfare! Also, do you think it is bad for me to enjoy a nice juicy Pink Lady now? If not, then why is it bad for someone to come into existence and only do that?
Methodologically, rather than noting that the sadistic repugnant conclusion is countintuitive and then trying to conjure up theories that avoid it, I think it would make more sense to ask why the sadistic repugnant conclusion would be false. The Z lives are positive, so it is better for them to live than not. The value aggregates in a non-diminishing way—the first life adds as much value as the quadrillionth. This means that the Z population can have arbitrarily large value depending on its size, which means that it can outweigh lots of other things. In my view, it is completely wrongheaded to start by observing that a conclusion is counterintuitive and ignoring the arguments for it when building alternatives. This is an approach that has lead to meagre progress in population ethics over the last 30 years—can you name a theory developed in this fashion that now commands widespread assent in the field? The approach leads people to develop theories such as CLU, that commit you to holding that a life of positive welfare is negative, which is difficult to understand from a welfarist perspective.
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.