YouNotSneaky has a great post in which he calculates how big a "jerk" you have to be to oppose immigration. The answer – proven with considerable mathematical sophistication – is that the exact "jerk factor" depends on theta, the extent to which marginal utility diminishes with income. The results, which you are unlikely to see in the JPE, make me laugh (but note that others will be insulted) are graphed here. Read the whole thing for details on the calculations which do make a serious point.
Hat tip to Dani Rodrik.