The irrelevance is no eccentric conclusion of my own. Many others have remarked it. Speaking about a prominent subdiscipline of economics, Wassily Leontief, a Nobel Laureate in economics, wrote in an open letter to Science,
Page after page of professional economic journals are filled with mathematical formulas leading the reader from sets of more or less plausible but entirely arbitrary assumptions to precisely stated but irrelevant theoretical conclusions. . . . Econometricians fit algebraic functions of all possible shapes to essentially the same sets of data without being able to advance, in any perceptible way, a systematic understanding of the structure and the operations of a real economic system. (1982)
Similarly, Herman Daly, formerly a senior economist at the World Bank, and his co-author, theologian John Cobb, Jr., opine,
There are probably no important theoretical or policy debates that have been resolved by econometrics, which was supposed to provide the empirical test for resolving all disagreements. What happened, however, was that each side of any debate developed its own econometricians (or "economeretricians" as some critics have called them). (1994, p. 32)
And, again, the economic historians Ernesto Screpanti and Stefano Zamagni refer to
that habit, which has become almost a vice for a great deal of contemporary economic theory, of only analyzing simple and well-defined problems so as to allow the scholar to find clear "truths" without getting too mixed up in the facts. (1993, p. 36)
The flight into mathematics and other abstractions does not necessarily lure us into a fantasy world. Everything depends upon whether we keep firmly in mind the full-fleshed reality from which the abstractions were drawn. But the tendency, it seems, is all the other way. The corporate takeovers of the junk bond era, for example (according to a former player on Wall Street), "were often the result of a twenty-six-year-old apprentice investment banker playing with his computer rather than a move by someone who knew something about the industry" (Michael Lewis, quoted in Kuttner 1996, p. 184).
Indeed, the irrelevance of practical knowledge has been asserted explicitly, if lightheartedly, as when economist Alfred Kahn, upon becoming chairman of the Civil Aeronautics Board in 1977, famously said he knew nothing about airplanes, which to him were just "marginal costs with wings."
Everything is much neater when you can ignore the concrete character of the world, feed well-behaved numbers into your computer models, and let the computer's satisfyingly precise algorithms grind out their conclusions. The result is an elegant and rigorous system, laid out in axioms, equations, and compelling deductions. The only problem is that it doesn't describe the real world and certainly not a world worth striving for. Hinting at this aversion from reality, Charles Schultze once remarked,
When you dig deep down, economists are scared to death of being sociologists. The one great thing we have going for us is the premise that individuals act rationally in trying to satisfy their preferences. (Quoted in Kuttner 1996, p. 41)
But "rationally" does not mean for economists what you and I might mean by it. "Like a mechanism" and "mathematically describable" come closer to the intent.