It's effectively boycotting businesses and people who you don't feel a personal connection to. It's not their fault you didn't want to make friends with them.

Imagine you were selling some amazing product that was cheaper and better than all the competition. But half the world refused to buy it because they don't like America's foreign policy so they want to hurt American companies. Wouldn't you feel a bit annoyed? You'd certainly lose a lot of money, and people everywhere would miss out on your superior product.

Buying local is a small stab in the side of free trade, economic growth and fairness. The overall effect is to make the world operate more wastefully. Nevermind the harm it causes poor farmers in the 3rd world who depend on selling you things to keep themselves alive.