the costs of immigration

Greg Mankiw links to a George Borjas paper on immigration that identifies a serious side effect of immigration to America (illegal or legal):

Using data drawn from the 1960-2000 U.S. Censuses, we find a strong correlation between immigration, black wages, black employment rates, and black incarceration rates. As immigrants disproportionately increased the supply of workers in a particular skill group, the wage of black workers in that group fell, the employment rate declined, and the incarceration rate rose. Our analysis suggests that a 10-percent immigrant-induced increase in the supply of a particular skill group reduced the black wage by 3.6 percent, lowered the employment rate of black men by 2.4 percentage points, and increased the incarceration rate of blacks by almost a full percentage point.

I don't like supporting a policy that I know will directly harm a segment of American society that is already struggling. On the other hand, I believe that the costs of immigration are outweighed by the economic benefits that accrue both to society as a whole and to the immigrants themselves. The proper policy solution isn't to limit immigration, but to capture part of the economic windfall through taxation and use that revenue to provide support and opportunities for those that bear the brunt of the costs.