Peter Singer is famous for asserting relentlessly that individuals have a moral obligation to give to the worse off until utilities are equal (pardon the crude simplification).
Harry Frankfurt, in his essay “Equality as a Moral Ideal,” gives a compelling argument for why that’s not necessarily the case. His argument is as follows:
“Now there is another claim that might be made here, which may appear to be quite plausible but which is also mistaken: where some people have less tha enough, no one should have more than enough. If this claim were correct, then–in the example at hand–the extra unit should go to one of the two people who have nothing. But one additional unit of the resource in question will not improve the condition of a person who has none (note: this is according to an example he lays out before). By hypothesis, that person will die even with the additional unit. What he needs is not one unit but five.”
What we can conclude from Frankfurt’s argument is the sensible point that our obligations are not to quantity of distribution–equality–but to the extent to which it makes a difference. As Frankfurt puts it earlier on in the paper, what is morally important is for everyone to have enough.
Although I’m inclined to side with Frankfurt, I would point out that he and Singer are not necessarily at odds. Singer, for the sake of argument, assumes that further transfers of wealth up to the point of equality will make a difference for the worse off. Frankfurt gives an argument for why this is not the case, which seems intutively reasonable although I don’t have a strong enough of a grasp on the argument to reproduce it here.