Traditionally, population ethics tends to assume that each person’s life has some utility value and then applies a simple aggregation formula to determine the overall value of the population. However, this idea assumes that people are separate and can be individually added and removed without affecting the utility of others. However in reality, the nature of society is that people are actually interconnected to each other such that every relationship and interaction can add or subtract utility to another person’s daily life experience. Furthermore, there are large consequential interactions such as future children who wouldn’t exist but for the existence of their ancestors, and the shared cultural inheritance that past generations give to future generations.
When you factor in these considerations, it becomes apparent that the overall utility of a life should not be thought of simply as an individual’s happiness minus suffering, but should also include the overall net utility of the consequences of their actions on others as well. This means that adding an individual to the population will actually interact with existing people’s utility and change them, as would subtracting one. How this plays out is dependent on many factors, such as the individual’s tendency towards cooperative, altruistic behaviour versus competitive, selfish behaviour, as well as the available resources in the environment that will have to be split between people in some distribution.
In the extreme case of one person in the universe, there are far more resources available than could ever be reasonably utilized by this person due to the law of diminishing marginal utility. As such, it is more efficient to add more people until the point at which resources actually are fully utilized. At that point, any additional people will force rationing of resources, which would add a kind of utility overhead cost that would diminish the overall total utility beyond what might be naively expected. Furthermore additional people bring competitive pressures. It is likely that as the population grows increasingly dense, competition will increase relative to cooperation and negative interactions will begin to overwhelm positive ones.
This suggests that there is actually an optimal point of population that is less than the maximum carrying capacity of the environment. The repugnant conclusion therefore does not follow from a correct understanding of the situation. The repugnant conclusion assumes that resource constraints and utility scale linearly when there is reason to believe that this is not the case. Instead, there is an optimum population that is dependent on the scale of interconnections between people, as well as the available resources in the environment.
Thus, a way to properly imagine this would be to say there are 100 units of resource in the environment. Furthermore each individual can utilize up to 10 units of resource before diminishing marginal utility reduces the effective utility to zero. A population of 1 is thus effectively only a single +10. There are enough resources to increase the population to 10 with each at +10. Beyond that, each additional person added will not only decrease the individual utility, but do so in a way that is beyond the expected. Naively at population 11, one might expect the individual utilities to be +9.1, but due to interconnections we would expect there to be an additional cost due to competition and rationing that further reduces utility. This means that functionally, the optimum point is a population of 10. It is, in this world, not possible to achieve 100 population at +1.
Therefore, the optimum population is the minimum that fully utilizes the resources of the environment, given the law of diminishing marginal utility as a constraint.