Henry George on trade:
Free trade consists simply in letting people buy and sell as they want to buy and sell. It is protection that requires force, for it consists in preventing people from doing what they want to do. Protective tariffs are as much applications of force as are blockading squadrons, and their object is the same—to prevent trade. The difference between the two is that blockading squadrons are a means whereby nations seek to prevent their enemies from trading; protective tariffs are a means whereby nations attempt to prevent their own people from trading. What protection teaches us, is to do to ourselves in time of peace what enemies seek to do to us in time of war.
Sadly, this insight keeps being relevant.