Immigration to relieve poverty

From Kerry Howley at Reason:

Wage gaps between observably identical Nigerian workers in the United States and Nigerian workers in Nigeria (same gender, education, work experience, etc) are... considerable. They swamp the wage gaps between men and women in the US. They swamp the gaps between whites and blacks in the US. Actually, they swamp the wage gaps between whites and blacks in the United States in 1855. For several countries, the effect of border restrictions on the wages of workers of equal productivity "is greater than any form of wage discrimination (gender, race, or ethnicity) that has ever been measured." The labor protectionism that keeps poor workers out of rich countries upholds one of the largest remaining price distortions in any global market.

Who cares? You weren't planning on seeking employment in Nigeria anyway. The upshot is that even a very limited loosening of borders could do enormous, immediate good. No other poverty alleviation policy--microcredit, education, public health interventions, anti-sweatshop activism--compares with a work visa, even a temporary one.