An important difference between the analogy you gave and our real situation is that non-Americans actually exist right now, whereas future human generations do not yet exist and they may never actually come into existence—they are merely potential. Their existence depends on the choices we make today. A closer analogy would be choosing an 80% chance of making all humans immortal and a 20% chance of eliminating the possibility of future space colonization. Framed this way, I don’t think the choice to take such a gamble should be considered selfish or even short-sighted, though I understand that many people would still not want to take that gamble.
An important difference between the analogy you gave and our real situation is that non-Americans actually exist right now, whereas future human generations do not yet exist and they may never actually come into existence—they are merely potential. Their existence depends on the choices we make today. A closer analogy would be choosing an 80% chance of making all humans immortal and a 20% chance of eliminating the possibility of future space colonization. Framed this way, I don’t think the choice to take such a gamble should be considered selfish or even short-sighted, though I understand that many people would still not want to take that gamble.