What do chocolate eggs have to do with U.S. trade policy?

“Here’s your dessert,” said economist Douglas Irwin, tossing a couple bags of the foil-wrapped treats to his luncheon audience Tuesday at the University of Chicago’s Booth School of Business.

Irwin said the candy used to be made in the United States. Now it comes from Canada, which unlike the U.S. doesn’t impose tariffs on imported sugar that raise manufacturers’ costs.

Irwin said tariffs and other protectionist trade policies might help some U.S. industries and workers. But they are “bad economics and bad foreign policies” that cause much more harm than good.

While there are 147,000 steelworkers in the U.S., Irwin said 6.5 million other workers in industries that use steel could be hurt by measures to protect the U.S. steel industry. And, while 135,000 textile workers might benefit from measures to stem imports, 44 million low income Americans could be hurt by higher prices.

Measures against specific countries, like Mexico or China, could backfire because other countries have ways of retaliating against the U.S. U.S. farm goods play a crucial role in trade, so that could be especially painful for U.S. farmers.

“Mexico has a choice,” Irwin noted. “Do they buy corn from the U.S. or from Argentina? It’s the same with China and soybeans.”

“If we start closing our markets, other countries will start closing theirs to us.”

Irwin’s presentations on trade came during a week when disputes between the U.S. and Canada were topping business headlines. It’s hardly the first time the two countries went head-to-head over trade.

Holding a copy of the Smoot-Hawley Tariff of 1930, he noted how the measure triggered retaliation from Canada. That was the part of a spiral of protectionism around the world that deepened the global economic stress already underway during the Great Depression.

“We thought it would help the U.S. economy,” Irwin said of the law. “It didn’t”

Instead of using trade protections to help workers, he backed other ideas:

Many of the job losses in manufacturing were caused not by trade, but by improvement in productivity, Irwin said. Protectionist trade measures “won’t help displaced workers, and won’t bring back the economy of the 1950s and 1960s.”