These so-called “paper sons” had spent considerable time studying the background of their supposed ancestors … (Carol Nolte, “Legacy of hope and despair,” p. A1, San Francisco Chronicle, Jan 21, 2010)

“So-called” already warns the viewer that something hatched, cooked up, played with, or unfamiliar is going to come up; putting quotation marks around the following term is bad style. Not simply bad style, but double emphasis, which only confuses the reader. Either dispense with “so-called” or remove the quotes—let the text flow.