Matt Lutz in Persuasion:
In Peter Singer’s paper, “Famine, Affluence, and Morality,” Singer defends two core moral propositions. The first is that “suffering and death from lack of food, shelter, and medical care is bad.” That should be uncontroversial. Singer doesn’t even argue for it, simply saying that if you disagree with that claim, you’re not his target audience. The second proposition is that “if it is in our power to prevent something bad from happening, without thereby sacrificing anything of comparable moral importance, we ought, morally, to do it.”
Singer illustrates this second proposition with the following thought experiment: suppose you are walking near a shallow pond and see a young child drowning. Unless someone jumps in to rescue the child, he will die. If you jump in, you can easily save him. However, you’re wearing very nice, expensive clothes, and those clothes will be ruined if you jump in. If you save the drowning child, you will prevent something bad from happening, and you will have to sacrifice to do it. But the thing that you will sacrifice, your nice clothes, is not of comparable moral importance to the life of a child. So you ought, morally, to save the child. If you don’t, you’re doing something profoundly morally wrong.