Why might trade barriers be a highly ineffective technique for increasing domestic employment?

What will be an ideal response?

First, trade barriers lower living standards by making consumer goods more expensive. This means that consumers have less to spend on everything including domestic goods. Second, trade barriers invite retaliation that can hurt our exports and those employed in export industries. Even without retaliation, in the long run exports are hurt as foreigners have fewer dollars to spend on American goods since their imports to the U.S. have declined. Third, barriers limit the advantages to be gained by specializing in production where costs are relatively lower and prevent attaining the lower costs which specialization allows.
If the world has a more efficient allocation of resources and a higher level of material well-being as a result of free trade, it follows that in the long run barriers would reduce output and incomes throughout the world. A nation can have full employment with or without free trade, but without free trade workers will be employed less productively and their incomes will be lower.