But of course the A and Z populations are already impossible, because we already have present and past lives that aren’t perfectly equal and aren’t all worth living. So—even setting aside possible boundedness on the number of lives—the RC has always fundamentally been about comparing undeniably impossible populations
I don’t find this a compelling response to Guillaume’s objection. There seems to be a philosophically relevant difference between physical impossibility of the populations, and metaphysical impossibility of the axiological objects. We study population ethics because we expect our decisions about the trajectory of the long-term future to approximate the decisions involved in these thought experiments. So the point is that NU would not prescribe actions with the general structure of “choose a future with arbitrarily many torturous lives and a sufficiently large number of slightly more happy than suffering lives [regardless of whether we call these positive utility lives], over a future with arbitrarily many perfectly happy lives,” but these other axiologies would. (ETA: As Michael noted, there are other intuitively unpalatable actions that NU would prescribe too. But the whole message of this paper is that we need to distinguish between degrees of repugnance to make progress, and for some, the VRC is more repugnant than the conclusions of NU.)
I don’t find this a compelling response to Guillaume’s objection. There seems to be a philosophically relevant difference between physical impossibility of the populations, and metaphysical impossibility of the axiological objects. We study population ethics because we expect our decisions about the trajectory of the long-term future to approximate the decisions involved in these thought experiments. So the point is that NU would not prescribe actions with the general structure of “choose a future with arbitrarily many torturous lives and a sufficiently large number of slightly more happy than suffering lives [regardless of whether we call these positive utility lives], over a future with arbitrarily many perfectly happy lives,” but these other axiologies would. (ETA: As Michael noted, there are other intuitively unpalatable actions that NU would prescribe too. But the whole message of this paper is that we need to distinguish between degrees of repugnance to make progress, and for some, the VRC is more repugnant than the conclusions of NU.)