You're pushing the idea of the discount rate beyond its underlying assumptions. Short-term temporal discounting is premised on two concepts:
1) A pseudo-psychological principle that people value things more in the present than in the future;
2) An economic principle rooted in the assumption that there are alternative investments available for any given expenditure.
(1) is problematic because: a) it's not true at the scales we're talking about; and b) it's intrinsically tied to how someone existing in the present values future benefits. It takes a very narrow view of "utility" to argue that only the value to those in the present is relevant.
(2) is problematic because the assumption isn't necessarily true. Imagine a world where there are no investments that yield a consistent return such that an investment at time T0 yields exponentially increasing wealth at time T0+T. In such a world the second principle provides no reason to engage in temporal discounting. At the scales we're talking about, this second principle starts to break down. You can't assume that an investment in the present will continue to yield returns indefinitely into the future if your actions result in their being no future humans.
I think a more apropos basis for a guiding principle in this area is the observation that, in absolute terms, the productivity of society grows exponentially. A single person 1,000 years from now will produce much more, in absolute terms, than a single person today. If we define our metric more objectively, something as the sum of all production over the existence of humanity, then the proper course of action is the one that preserves as many future lives as possible, even at the expense of present lives, because most production will happen in the future.
(1) is problematic because: a) it's not true at the scales we're talking about; and b) it's intrinsically tied to how someone existing in the present values future benefits. It takes a very narrow view of "utility" to argue that only the value to those in the present is relevant.
(2) is problematic because the assumption isn't necessarily true. Imagine a world where there are no investments that yield a consistent return such that an investment at time T0 yields exponentially increasing wealth at time T0+T. In such a world the second principle provides no reason to engage in temporal discounting. At the scales we're talking about, this second principle starts to break down. You can't assume that an investment in the present will continue to yield returns indefinitely into the future if your actions result in their being no future humans.
I think a more apropos basis for a guiding principle in this area is the observation that, in absolute terms, the productivity of society grows exponentially. A single person 1,000 years from now will produce much more, in absolute terms, than a single person today. If we define our metric more objectively, something as the sum of all production over the existence of humanity, then the proper course of action is the one that preserves as many future lives as possible, even at the expense of present lives, because most production will happen in the future.