YouNotSneaky! calculates how big a jerk you have to be to be anti-immigration. Here’s how he frames his thought experiment:

This kind of argument provokes the expected response from the expected folks, roughly along the lines that we should care more about native workers – the citizens – then the migrants – the non-citizens. Ok. But how much more? Let’s put on our annoying-economist hat and consider the question; if you consider a foreign national to be only 1/2 a human being (alright, alright, only 1/2 as “important”) as a native citizen, are you justified in opposing immigration? After all, it takes a real jerk to argue that foreign people’s welfare should not count at all. Suppose the foreigners are only 1/10th as important? Surely, if natives’ welfare counts for ten times as much as that of foreigners, we would be justified in banning immigration since it may adversely affect the wages of the unskilled in US? Well, let’s see…

Seeing how he arrives at an answer is more than half the fun, so I’ll leave it to you to follow the link. (Via Marginal Revolution)