For more than a century, this country enjoyed the benefits of increased productivity, paralleled by rising paychecks for working men and women. It seemed fair enough: You made more widgets, you earned more money, and the boss got richer at the same time. This implicit social contract began to disintegrate in about 1980. Since then, productivity has continued to increase apace. But wages have stagnated, and the gap between workers and the rich has grown to record levels. At the same time, our fabled American land of opportunity has become a place where, if you are born poor, you will …