The rest of the world has trade barriers...a tariff by any other name for most products. Why should our markets be open while other countries are closed?
If another country chooses to mis-allocate capital, so that it places it’s limited resources in industries which are less than competitive on a world market basis, it reduces it’s total wealth in the long run. That’s why. As Napoleon said, “When your enemy is making a mistake, don’t interrupt him.”