Consider two men, A and B. Man A steals food because he’s starving to death, while Man B commits a rape because no woman will agree to have sex with him.
From a Darwinian perspective, the two cases seem exactly analogous. In both we have a man on the brink of genetic oblivion, who commandeers something that isn’t his in order to give his genes a chance of survival. And yet the two men strike just about everyone — including me — as inhabiting completely different moral universes. The first man earns only our pity. We ask: what was wrong with the society this poor fellow inhabited, such that he had no choice but to steal? The second man earns our withering contempt.
Befuddled by his genes-eye view, Scott asks: "can any of you pinpoint the difference between the two cases, that underlies our diametrically opposite moral intuitions?" Of the 80-odd responses, only two or three struck on the answer (though no-one listened): try looking at it from a human perspective.
Many noted the obvious point that rape generally inflicts far greater harm than stealing a loaf of bread. But this is an inessential point, as Robin notes: "it might help to imagine a society where the person who lost the food was also in some, though less, danger of starving. But even then food and sex seem to be treated differently."
A related reason is that - consequences aside - they're actually very different kinds of acts. It's misleading to describe both merely as an instance of "commandeer[ing] something that isn’t his", because very different kinds of 'ownership' are being violated. Our intuitions reflect the fact that material property rights are - in a sense - "socially constructed", and if not done right they may fail to yield genuine (reasonable) obligations. In any case, there's no question that the actual distribution of material wealth in the world is historically contingent. A person's self-ownership, by contrast, is a more essential matter. Rape is not just "theft of a body", but a deeply personal violation.
But the central mistake, I'd suggest, is to think that there's any relevant similarity between the motivations for either act. A person does not really act "in order to give his genes a chance of survival." This simply illustrates the all-too-common confusion of biological and psychological teleology. What matters for moral assessment are the real psychological motives of people, not the metaphorical "motives" we attribute to their genes.
From a person's perspective, then, the "analogy" is a non-starter. The starving man needs to eat in order to survive -- a likely precondition for realizing any of his other values. The vital importance of this is beyond question. The second man's "need" for sex is hardly comparable. (It's perfectly possible for the celibate to still lead worthwhile lives.) So, only one of them has a genuine need that could reasonably justify imposing such burdens on others.
It's worth emphasizing that genetic 'goals' don't really have any moral significance, as ethics is instead concerned with the welfare of persons (psychological beings). I'm amazed by how easily evolutionary psychology can lead otherwise intelligent people to lose sight of this basic fact.
But, this particular pseudo-puzzle aside, I do think Robin is right to note that "our concern about inequality is not very general": we focus almost entirely on material inequality, even though non-financial factors arguably have a greater impact on welfare once our basic needs have been met. Should we also be concerned about the distribution of popularity, status, attractiveness, charisma, etc.? How about discrimination due to eccentricity, social awkwardness, or simple introversion? (There's no denying it's an extrovert's world!) It's harder to imagine how to address these matters, I suppose...