"[M]ost of us would readily concede that the framers of the 1787 Constitution adopted a federal system of government organization in order to, among other goals, help secure the institution of private property. When Madison, in his theory of faction, suggested that shifting the legislative responsibility for certain problems from the state to the national level could help assure that majorities would not trample on minority rights, the problems he had in mind were largely economic; the minority rights... were, for the most part, rights of property and contract."