Jonah: Your correspondent makes many of the usual mistakes:

1. The overall unemployment rate is irrelevant to this debate. What’s important is the rate for Americans with less than high school, since that’s the group facing the most competition with immigrants; their unemployment rate is around 14 percent.

2. Among construction workers, native-born unemployment in 2005 was 11.3 percent, and natives make up almost three-fourths of the workforce (see Table 5 here).

3. The illegal workforce couldn’t be “suddenly shut down” even if we wanted to — the question is whether we want to shrink it over a period of several years by beginning to enforce the law, allowing the market to compensate.

4. Employers, even sincere ones, often can’t see the forest for the trees. At a Senate hearing in 1916, a mill owner said that limiting child labor would “stop my machines”; another said “investors would never receive another dividend”; while a third said that ending child labor would “paralyze the country.” Not using child labor has become a labor standard (without any of the ridiculous predictions coming true); the economy will also adjust to making legal status a similar labor standard.