Does illegal immigration help or hurt the U.S. economy? It sounds like a simple enough question. But, like the classic Japanese movie "Rashomon," in which truth depends entirely on point of view, the answer hinges on where you fit in the economy. "GDP per domestic person goes up," said James Smith, a senior economist at the Rand think tank in Santa Monica and lead author of the National Research Council's study "The New Americans: Economic, Demographic and Fiscal Effects of Immigration." Since 1980, he said, all immigrants, including both undocumented and legal, have boosted GDP by $10 billion per year....