This philosophy also presumes that the future existence of these trillions of hypothetical humans is an inherent good, when it seems to me that they would not be alive to lament their nonexistence (indeed, they may as well be spared from suffering in a miserable world), and so the ethical calculus falls upon the set of humans currently alive to determine how valuable that scenario is to them.

Am I meant to believe that the average human currently alive values an intergalactic future at thousands of times the value derived from their own existence? For the vast majority of people, that factor is probably in the ones and twos at most. I can think of many people I know personally for whom that factor is marginally negative.