Isn't this just the Thanos argument, though? Given the huge number of possible future lives under space colonization, all of them ending inevitably in death and suffering, no amount of trying to improve those lives can ever has as much of a positive impact as just avoiding them by pushing for, say, nuclear self-annihilation now, because the somewhat larger suffering for a much, much smaller number of people is a higher "expected value"? I'm not really keen on moral arguments that end up arguing for nuclear war…