Do Illegal Immigrants Take Jobs and Lower Wages in the United States?

Tyler Cowen, who blogs at Marginal Revolution, has published a commentary piece in today's Los Angeles Times. He and his coauthor, Daniel M. Rothschild, ask if "unskilled" laborers siphon jobs and depress wages. Here's part of the introduction:

Recent public discourse would have us believe that they [unskilled workers] poach American jobs, lower wages and sponge off welfare. Yet economic research suggests a different picture: Unskilled immigrants are good for the U.S., and the U.S. is good for them. Until the late 1990s, when a boom in native-born self-employment occurred, immigrants were more likely than natives to work for themselves. Immigrant small businesses, from the Korean corner market to the Mexican landscaping service, are, well, as American as apple pie. The labor market is not a zero-sum game with a finite number of jobs; immigrants create their own work. A key question for economists has been whether the influx raises or lowers "native" American wages. UC Berkeley's David Card, who studied patterns in different U.S. cities, concludes that immigration has not lowered wages for American workers. George Borjas of Harvard counters that immigration reduced the wages of high school dropouts by 7.4% between 1980 and 2000. Most economists have sided with Card. For one thing, his studies better capture the notion that immigrant labor makes work easier for all of us and brings new skills to the table. Additionally, as Card points out, the percentage of native-born high school dropouts has fallen sharply over the previous decades, creating a shortage of unskilled laborers that immigrants fill. In 1980, one in three American adults had less than a high school education; by 2000, this figure had fallen to less than one in five.

What's interesting about the piece is its neutral nominalism. Is it "unskilled immigrants" most people are taking about in the current illegal immigration debate? Or is it "illegal aliens" or "undocumented laborers" who so concern reformers and the public. As Cowen and Rothschild note, immigration provides a net benefit to the U.S. in economic activity, and some argue that continuing high rates of immigration will provided a broader tax base to maintain the Social Security entitlment system. Nevertheless, the legal/illegal distinction in the debate, in addition to the skilled/unskilled dimension, might be more clearly highlighted.