The Economist's Free Exchange blog calls attention to Russel Roberts' short essay Why We Trade:
To hear most politicians talk, you’d think that exports are the key to a country’s prosperity and that imports are a threat to its way of life. Trade deficits—importing more than we export—are portrayed as the road to ruin. U.S. presidential hopefuls Hillary Clinton and Barack Obama want to get tough with China because of “unfair” trading practices that help China sell products cheaply. Republican candidate Mitt Romney argues that trade is good because exports benefit the average American. Politicians are always talking about the necessity of other countries’ opening their markets to American products. They never mention the virtues of opening U.S. markets to foreign products.

...

We don’t export to create jobs. We export so we can have money to buy the stuff that’s hard for us to make—or at least hard for us to make as cheaply. We export because that’s the only way to get imports. If people would just give us stuff, then we wouldn’t have to export. But the world doesn’t work that way.

It’s the same in our daily lives. It’s great when people give us presents—a banana bread or a few tomatoes from the garden. But a new car would be better. Or even just a cheaper car. But the people who bring us cars and clothes and watches and shoes expect something in return. That’s OK. That’s the way the world works. But let’s not fool ourselves into thinking the goal of life is to turn away bargains from outside our house or outside our country because we’d rather make everything ourselves. Self-sufficiency is the road to poverty.

And imports don’t destroy jobs. They destroy jobs in certain industries. But because trade allows us to buy goods more cheaply than we otherwise could, resources are freed up to expand existing opportunities and to create new ones. That’s why we trade—to leverage the skills of others who can produce things more effectively than we can, freeing us to make things we otherwise wouldn’t be able to afford.
Read the whole thing.

Incidentally, one of the people responsible for this fear-mongering (probably stemming from genuine beliefs) on behalf of the politicians is the distinguished idiot economist, Lester C. Thurow. His 1995 book, The Future of Capitalism, well nigh predicted a global catastrophic meltdown of capitalism imminent 'any day now', with the U.S. trade deficit being one of a number of causes. He's the same guy who wrote in 1989, just before the Soviet Union imploded:
Can economic command significantly... accelerate the growth process? The remarkable performance of the Soviet Union suggests that it can... Today the Soviet Union is a country whose economic achievements bear comparison with those of the United States.