It eases pressure to automate AND compensates for revenue shortfalls.

There are two sound arguments for taxing robots. The easiest is this: Governments need the money. In the United States, income taxes account for half of the $3 trillion collected every year by the Internal Revenue Service; payroll taxes account for another third.

Imagine that the fears about robots taking over jobs actually come true. Two years ago, the McKinsey Global Institute found that the job functions that are “most susceptible to automation” in the United States account for 51 percent of the activities in the economy and $2.7 trillion worth of wages. The institute estimates “half of today’s work activities could be automated by 2055.” If that happens, hundreds of billions of tax dollars would be lost every year.

And at the same time that the rise of robots shrinks government tax revenue, the fallout from automation will place more demands on government services. The United States will probably need more money to retrain workers bumped from their jobs by automation, to give them a shot at a new one. Welfare rolls could grow, as millions of workers are displaced to the bottom end of the service economy, where wages are low and robots are scarce.

To afford any kind of government services in the robot era, governments will have to find something else to tax. Why not the robots themselves?

The case for taxing robots is stronger when you consider that a lot of automation these days is not deployed to enhance economic productivity. Instead, many businesses are investing in automation simply because the tax code is urging them to do so.

The purpose of taxing robots is not simply to stop them from killing jobs. It is to level the playing field, to ensure that investments in automation raise productivity.

“The tax system incentivizes automation even in cases where it is not otherwise efficient,” wrote Ryan Abbott and Bret Bogenschneider of the University of Surrey School of Law in Britain, in an analysis of tax policy toward automation in the United States and other rich countries. “The vast majority of tax revenues are now derived from labor income, so firms avoid taxes by eliminating employees.”

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Daron Acemoglu, an economist at the Massachusetts Institute of Technology, explains that automation often produces benefits of dubious value to the business itself. More important, he suggests that the investment in technologies designed to replace workers has come at the expense of alternative investments that might find more productive uses for human labor. This may help explain the sluggishness in overall productivity growth across the economy.

One powerful reason that businesses deploy so many robots, despite their sometimes questionable contribution to the bottom line, is that automation is subsidized. “Subsidies induce firms to substitute capital for labor even when this is not socially cost-saving, though it is privately beneficial because of the subsidy,” Professor Acemoglu and his co-author, Pascual Restrepo, wrote.