Most of the things that are being pursued as longtermist interventions only require caring about our grandchildren, or maybe great grandchildren, which well within scope of even many ethical frameworks that care about preferences but not future lives. The rest of the interventions potentially require caring about the next, say, 1,000 years—which still doesn’t require anything like the actual longtermist assumptions. (Anything further out than that isn’t really going to be amenable to the types of actions we’re taking anyways.)
Most of the things that are being pursued as longtermist interventions only require caring about our grandchildren, or maybe great grandchildren, which well within scope of even many ethical frameworks that care about preferences but not future lives. The rest of the interventions potentially require caring about the next, say, 1,000 years—which still doesn’t require anything like the actual longtermist assumptions. (Anything further out than that isn’t really going to be amenable to the types of actions we’re taking anyways.)