Elizabeth Dwoskin considers various arguments:
The notion of jobs in fields and food plants as “immigrant work” is relatively new. As late as the 1940s, most farm labor in Alabama and elsewhere was done by Americans. During World War II the U.S. signed an agreement with Mexico to import temporary workers to ease labor shortages. Four and a half million Mexican guest workers crossed the border. At first most went to farms and orchards in California; by the program’s completion in 1964 they were working in almost every state. Many braceros—the term translates to “strong-arm,” as in someone who works with his arms—were granted green cards, became permanent residents, and continued to work in agriculture. Native-born Americans never returned to the fields. “Agricultural labor is basically 100 percent an immigrant job category,” says Princeton University sociologist Doug Massey, who studies population migration. “Once an occupational category becomes dominated by immigrants, it becomes very difficult to erase the stigma.”
Massey says Americans didn’t turn away from the work merely because it was hard or because of the pay but because they had come to think of it as beneath them.