While there is some debate, the evidence strongly suggests that economic liberalization and the removal of barriers to free trade is beneficial in the long term. However, the adjustment process and short-term damage of free trade is far more visible. Seeing jobs sent overseas is painful to watch, but ultimately it is for the better.
The debate typically stops there, however. The rallying cry is to always protect American workers. I think we might do well to remember two other benefits in particular:
1. Sending jobs overseas provides a source of income for the world's poorest people. Is their life less important because they are not American?
2. Fewer barriers to trade means more trade. And nothing stops conflict and war like economic ties. The more we trade with Africa and the Middle East, the more our interests become their interests.
A final quote from Winston Churchill:
"The inherent vice of capitalism is the unequal sharing of the blessings. The inherent blessing of socialism is the equal sharing of misery."