The recent tax cuts should be a net positive for the U.S. economy, but there is one statistic that has two University of Chicago professors concerned about its long-term future: the employment rate of 21- to 30-year-old millennials.

The national unemployment rate stand at 4.1 percent. The last two times it reached that level were in 2000 and 2007. In both those years, the unemployment rate for 21- to-31-year-olds was 6 percent.

Today it is 18 percent. That’s one indication of how many more millennials have checked out of the labor force versus past generations. Fully 70 percent of millennials not working are living in their parents’ home.

That development surfaced in a wide-ranging conversation between University of Chicago economics luminaries Erik Hurst and former Fed governor Randall Kroszner. What leaves them most concerned is that in past times of rapid change it always has been workers 50 years old and up who have found adjusting to change challenging and dropped out.

Kroszner noted that Hurst was working on a major paper on this subject and been offered a chance to see it, sounding as if he had been sllghted. But when talking about millennial labor market issues and the disappearance of productivity in the 21st century, both academics were convinced of one truism. Facebook is a "productivity killer."

Asked about whether the government statisticians calculating GDP might be missing some activity as the gig economy mushrooms, both professors said this hypothesis was false, adding that Uber and Airbnb revenues were fully reflected in the numbers. One wonders, however, about much smaller gig enterprises.

Other than that, both professors offered some positive insights into the current U.S. economy. Kroszner believes that cuts in the personal tax will increase American’s purchasing power by 3 percent. Full expensing of capital investments will incentivize companies to purchase both new software and machines.

But how much they will spend remains to be seen. Businesses are sitting on a tremendous amount of cash, which tells Hurst that there aren’t a “lot of viable options” out there. Kroszner added that just because Apple had hundreds of billions sitting in foreign banks, it didn’t constrain them from spending it.

What the tax cut won’t do is address the problems of inequality and the middle class, they said. Kroszner noted that the bottom half of the U.S. income distribution pays only 3 percent of all income taxes, so “it’s impossible for them to benefit equally from an [income] tax cut.”

Hurst added that he expected the effects of the tax cut on middle-class wage growth would be minimal.