The Self-Interest of Economists

An anonymous commentator on a previous post asks a good question about economists' motives:

About self-interest, I have always been wondering about this question: if economists are right that we should generally assume self-interest for rational actors, why should we believe in anything that economists say? Obviously, they say those things out of self-interest rather than respect for truth.

So what motivates me? Self-interest or respect for the truth?

The answer, I believe, is both.

Suppose I filled my blog and books with nakedly self-interested statements: "The world would be a happier and more prosperous place if everyone sent Greg Mankiw $20." First of all, no one would believe me. Second, people would stop reading my blog and buying my books. Making self-interested statements like this is not in my self-interest.

What is in my self-interest? Providing arguments and evidence about the truth. People read this blog and buy my books because they find the discussion of economic issues cogent or at least thought-provoking. My self-interest and relentless pursuit of the truth are not conflicting goals; they are two sides of the same coin.

Or maybe it's just in my interest to have you believe that.