Companies once felt an obligation to support American workers, even when it wasn’t the best financial choice,” said Betsey Stevenson, the chief economist at the Labor Department until last September. “That’s disappeared. Profits and efficiency have trumped generosity.” Companies and other economists say that notion is naïve. Though Americans are among the most educated workers in the world, the nation has stopped training enough people in the mid-level skills that factories need, executives say. To thrive, companies argue they need to move work where it can generate enough profits to keep paying for innovation. Doing otherwise risks losing even more American jobs over time, as evidenced by the legions of once-proud domestic manufacturers — including G.M. and others — that have shrunk as nimble competitors have emerged.