"Now, any economics textbook will tell you that it's fine to borrow from abroad if the money is used to expand the economy's productive capacity. When 19th-century America borrowed from Europe to build railroads, it was also enhancing its ability to repay its debts later. But we aren't borrowing to build productive capacity. As a share of G.D.P., investment other than housing construction is below its average between 1980 and 2000, and way below its level at the end of the 1990's."
Thanks to Brenda Meyer