Roger Crisp provides a thought experiment:
Imagine some group of beings like us, except that these beings cared much more about people born on Tuesdays than those born on other days. (Their so caring is a brute fact, and does not rest on, say, any religious or superstitious assumptions about Tuesdays.) Even sentimentalists about ethics will probably wish to claim that there is something dubious about this differential attitude. But that raises the question whether we should say the same about a preference for identifiable fellow-citizens.
The property of being an identifiable fellow-citizen is not clearly morally irrelevant in the way that being born on Tuesday is. Indeed, it seems similar in important ways to the property of being one’s child, and most of us think that this is a property of great moral relevance when we are deciding how to spend our scarce resources. But there is of course one big dissimilarity: in most cases, a parent has deep personal relations with a child, and these could be taken to ground a parent’s giving greater weight to the interests of her child over those of others. The fact that such a relationship is lacking in the case of identifiable fellow-citizens suggests that the property of being an identifiable fellow-citizen may well be morally as irrelevant as that of being born on a Tuesday.
The Dish 