Go back and read again. He's not saying anything that free markets are an imperfect way of delivering what people want, but they're better than anything else we've come up with. He's saying that free markets tell us what people want, and if you disagree with the "free market" (which is an abstraction, I don't think most things people refer to as free markets actually are the "free markets" of economic textbooks), you're disagreeing with what people actually want. That makes free markets right by tautology; the best is what people want, and what people want is what they buy on free markets. Which is fine if you want to short-circuit debate, but it doesn't actually let us ask the important questions.