The complexity of a free market is elucidated brilliantly in the essay I, Pencil by Lawrence Read. It should be included in every economics 101 textbook, right up front. The problem with most lib computations is not accuracy but insight. They treat the aggregate decisions of countless individuals, each working in his own self interest as a black box. They abstract away the negative feedback effect that their proposals exert. The magic phrase of the experimenter is "all things being equal". Where the calculations fall apart is that in the real world, all thinga are NEVER equal. Thus the observation that somewhat lower tax rates in reality produce more revenue and raising tax rates lowers revenues.