I usually agree with Bill Gates on matters of public policy and admire his emphasis on the combined power of markets and technology. But I think he went seriously astray in a recent interview when he proposed, without apparent irony, a tax on robots to cushion worker dislocation and limit inequality. The Microsoft co-founder is right about the gravity of the problem and need for action, but he’s profoundly misguided in his proposed solution – and in ways that point up problems with the current public debate. First, I cannot see any logic to singling out robots as job destroyers. What about kiosks that dispense airplane boarding passes? Word-processing programs that accelerate the production of documents? Mobile banking technologies? Autonomous vehicles? Vaccines that, by preventing disease, destroy jobs in medicine? There are many kinds of innovation that allow the production of more or better output with less labor input. Why pick on robots? Does Gates think anyone, let alone Congress, the Trump administration or a commission composed of his fellow technocrats, can distinguish labor-saving activities from labor-enhancing ones? Surely even if experts could draw such distinctions, the ability of the Internal Revenue Service to administer them is in doubt. Second, much innovative activity, even of a robotlike variety, involves producing better goods and services rather than simply extracting more output from the same input. Autonomous vehicles will likely be safer than ones driven by humans. Robotics already help surgeons perform certain operations better than they can on their own. Online reservation systems are faster and more convenient than travel agents. Moreover, because of emulation and competition, innovators capture only a small part of the benefit of their innovation. It follows that there is as much a case for subsidizing as taxing types of capital that embody innovation. Third, and perhaps most fundamentally, why tax in ways that reduce the size of the pie rather than ways that assure that the larger pie is well-distributed? Imagine that 50 people can produce robots who will do the work of 100. A sufficiently high tax on robots would prevent them from being produced. Surely it would be better for society to instead enjoy the extra output and establish suitable taxes and transfers to protect displaced workers. It is hard to see why shrinking the pie, rather than enlarging it as much as possible and then redistributing, is the right way forward. This last point has long been standard in international trade theory. Indeed, it is common to point out that opening a country to international trade is like giving it access to a technology for transforming one good into another. The argument, then, is that since one surely would not regard such a technical change as bad, neither is trade, and so protectionism is bad. Gates’s robot tax risks essentially being protectionism against progress.