A 2006 poll of Ph.D. members of the American Economic Association found that 87.5 percent agreed that “the U.S. should eliminate remaining tariffs and other barriers to trade.”
The benefits from an open world trading system are standard fare in introductory economics courses...The basic lessons can be traced back to Adam Smith of the 18th century and David Ricardo of the 19th century
As an argument for free trade goes, this one is weak. In effect, Mankiw is saying, "Economists are for free trade, so you should be, too."
The challenge is to make an argument for free trade in terms that everyone can understand. Perhaps a parable is in order. Perhaps we could start with "Once upon a time," and describe an economy that works like ours today. But we decide that free trade has gone too far.
First, we enact national protectionism. Then, the "buy local" movement catches on and leads to effective elimination of the Constitutional provisions against trade barriers within the United States. Cities and states start enacting tariffs, quotas, and trade subsidies.
Finally, the movement moves toward its logical conclusion: only buy products made in your own household. People give up computers, cars, packaged food, electricity, and plumbing. We go back to subsistence farming and hunter-gathering.