Here's the math, for those who like this sort of thing. If the utility from an extra dollar is inversely proportional to your income, we can assume that utility is given by the log of income. If N Americans earning $10 an hour lose $e an hour each, the utility loss is N Log(10) - N Log(10-e). If Ne = $3 per hour (as in the column) and if N is large, this expression is approximately 3/10. For the immigrant, the utility gain is Log(9)-Log(2), or approximately 1.5, which is five times as much.