BusinessPundit references a good article that appears on Capital Magazine entitled "The Folly of Protectionism."
Key points from the article:
"Many think of free trade in terms of nations doing business. One hears that America has so many millions of dollars worth of trade with Taiwan, for example, and so many millions with Singapore. But actually the commerce is between companies, not countries.
Indeed, when protectionists seek to block imports-- often under the banner of "patriotism"-- what they're really blocking is the free exercise of property rights. And there's nothing American about that.
Protectionism is as wrong in practice as it is in theory. Just as you're better off "importing" goods into your house from stores rather than laboring to produce everything yourself within the borders of your home, so too is a nation better off observing that same principle.
Consider that if it were true that imports from other nations hurt America, that principle would also apply to goods imported into one state from another, and into one county, city or municipality from another county, city or municipality.
Bottom line: protectionism fully implemented across all industries would mean a lower standard of living, because it would result in capital and labor unnecessarily being diverted into the production of goods that could more economically be produced elsewhere."