The paradigms a person uses (or assumes) while thinking about anything determines the conclusions reached. The choice of an incorrect paradigm usually renders the thought process invalid.
Free trade was practiced long before restricted trade. Restrictions were placed on trade to prevent the damage done to domestic producers by allowing free trade with foreign producers. The elimination of these restrictions on free trade has reintroduced the damage the restrictions had been introduced to prevent. A careful examination of paradigms would have avoided this malign consequence.
The basic paradigm of free trade is this: Country A produces products for domestic consumption, but it produces more than the nation can consume. The excess production is sent to country B where no similar product is produced to be sold there. Country B does the same thing with a different product. Both nations are enriched by the trade. The excess production is gainfully sold and each nation gets access to a product it did not itself produce. The earliest example of such trade is European trade with China. European made metal utensils were sent to China to be traded for silk cloth. Metal utensils for the Chinese, silk cloth for the Europeans–win win.