Maybe you need some account of transworld identity (or counterparts) to match these lives across possible worlds
That’s the concern, yeah. When I said ”some nontrivially likely possible world containing an astronomical number of happy lives”, I should have said these were happy experience-moments, which (1) by definition only exist in the given possible world, and (2) seem to be the things I ultimately morally care about, not transworld persons.[1] Likewise each of the experience-moments of the lives directly saved by the AMF donation only exist in a given possible world.
That’s the concern, yeah. When I said ”some nontrivially likely possible world containing an astronomical number of happy lives”, I should have said these were happy experience-moments, which (1) by definition only exist in the given possible world, and (2) seem to be the things I ultimately morally care about, not transworld persons.[1] Likewise each of the experience-moments of the lives directly saved by the AMF donation only exist in a given possible world.
(Or spacetime regions.)