What if it's about who can make others sacrifice, and just not do so themselves? What if we don't want to reduce impact? What happens when the strong do what they can, and the weak suffer what they must? It's inevitably going to be a conflict over resources and power, like all of human history. Those who willingly self-sacrifice will get dominated by those who do not. Then what? Appeals to universal morality will only work to diminish those who agree to follow them and strengthen those who don't.