I'm often denounced for drawing attention to the salience of race and ethnicity to immigration policy. Under an ideal immigration system -- limited numbers of legal immigrants chosen for their high human capital rather than for family connections -- race and ethnicity would be much less relevant a question.
Highly skilled immigrants without extensive family connections already in the U.S. tend to blend in well to middle class suburban America. Moreover, the fat life in America can corrupt people -- look at the horrible rates of obesity and diabetes seen in many long-established Mexican-American communities, such as in South Texas. Similarly, among Hispanics, the illegitimacy and crime rates go up in subsequent generations. (For Latinos, overall, illegitimacy is about twice the Anglo white rate, and the imprisonment rate is three times as high -- and 13 times as high as the Asian-American rate.)
So, if we thought rationally about immigration, we would want to bring in people with the most human capital to start with so their descendents would be well set to withstand the morally degrading temptations of American life.
In contrast, the current system of massive illegal immigration and most legal immigration driven by "family reunification" makes race and ethnicity extremely useful predictive markers. Because we aren't choosing Mexicans, they are choosing for us, we are getting run of the mill Mexicans. Although there is a lot of hopeful chatter about how the latest Mexican illegals are going to turn into Italians Real Soon Now, that kind of talk is a lot more persuasive to members of the media elite in DC and NYC, where Mexicans are new and exotic, than in parts of the country that have had huge Hispanic presences for many generations, such the Upper Rio Grande Valley of New Mexico, the Lower Rio Grande Valley of Texas, and Southern California. Recall Tim Russert's recent humiliation of New Mexico governor Bill Richardson for New Mexico's dismal rankings on most measures of human welfare -- and that's after 159 years of Hispanic assimilation into the U.S. Richardson didn't suddenly make New Mexico an underachiever of a state -- it's always been that way due to the human capital of the inhabitants.
No wonder Barack Obama is leading the charge against the one good thing in the Senate immigration bill -- the attempt at reforming and rationalizing the current system of legal immigration along the Canadian point-system model. His whole early career was devoted to racially divisive politics, and immigration is a good way to add to the divisions with American society. It's good for politicians, bad for Americans.