From Bureaucracy, by Ludwig von Mises:
Whether one likes it or not, it is a fact that the main issues of present-day politics are purely economic and cannot be understood without a grasp of economic theory. Only a man conversant with the main problems of economics is in a position to form an independent opinion on the problems involved. All the others are merely repeating what they have picked up by the way. They are an easy prey to demagogic swindlers and idiotic quacks.
Their gullibility is the most serious menace to the preservation of democracy and to Western civilization. The first duty of a citizen of a democratic community is to educate himself and to acquire the knowledge needed for dealing with civic affairs. The franchise is not a privilege but a duty and a moral responsibility. The voter is virtually an officeholder; his office is the supreme one and implies the highest obligation. A citizen fully absorbed by his scientific work in other fields or by his calling as an artist may plead extenuating circumstances when failing in this task of self-instruction. Perhaps such men are right in pretending that they have more important tasks to fulfill. But all the other intelligent men are not only frivolous but mischievous in neglecting to educate and instruct themselves for the best performance of their duties as sovereign voters.
See also Bryan Caplan's two-part essay, "Mises and Bastiat on How Democracy Goes Wrong", contrasting Mises's view with Bastiat's on the question of democracy and economic understanding: Part I, Part II.