I think the argument can be expanded into a general point about the linkage between moral and political philosophy. Consider two important questions, the first usually considered a matter of moral philosophy, the second a matter of political philosophy:
1. What beings (adults, children, fetuses, animals, aliens, etc.) are deserving of moral consideration? Call this the question of moral personhood.In intellectual circles, we usually regard moral philosophy as preceding political philosophy. We therefore address these two questions either (a) separately, or (b) in that order. We decide who constitutes a moral person – whose rights or interests therefore deserve consideration – and then we talk about the political status of such persons. But in practical politics, I think people consciously or unconsciously answer these questions using a kind of backward induction, considering political status first and then moral personhood. That is, they begin by asking what rights, privileges, and powers will be accorded to persons within a political system, and then (taking the previous answer as given) they decide who ought to be regarded as a person and to what extent.
2. What political rights, privileges, and powers should beings with moral personhood have? Call this the question of political status.
Thus, in the case of the immigrant, intellectuals will likely start from the (seemingly obvious) point that immigrants are people just like us, and therefore their interests should have just as much weight as ours. But most people will start with the question of what kind of political system is in place. If it’s a welfare state, this will dispose them to regard native-born citizens as having interests that supersede those of immigrants.
The significance for moral philosophy, I think, is that economic incentives affect people’s moral judgments in ways that we cannot reasonably ignore. It’s all well and good to say that other people’s (and sentient beings’) interests count. It’s another thing entirely to get people willingly to respect those interests.
As Ludwig von Mises emphasized in Human Action, love and respect for one’s fellow man is the result, not the cause, of social cooperation. In the absence of cooperation, “Each man would have been forced to view all other men as his enemies; his craving for the satisfaction of his own appetites would have brought him into an implacable conflict with all his neighbors. No sympathy could possibly develop under such a state of affairs” (p. 144). If we wish to encourage people to regard other moral beings as equals and not enemies, we should favor social systems that foster cooperation rather than creating conflicts of interest.
This is, by the way, the serious point I try to make in my article, “The Political Economy of Non-Coercive Vampire Lifestyles,” forthcoming in The Undead and Philosophy. More on that topic here.