Mexican Exceptionalism

Ross describes the downsides to having a whopping 57% of illegal immigrants come from one country:

A more diverse immigrant population would have fewer opportunities to self-segregate and stronger incentives to assimilate. Fears of a Spanish-speaking reconquista would diminish, and so would the likelihood of backlash. And instead of being heavily skewed toward low-skilled migrants, our system could tilt toward higher-skilled applicants, making America more competitive and less stratified.