Arguments for protectionism?
Global supply and demand. If one nation imposes trade restrictions on another a snowball effect occurs negatively throughout the global trade network. The decrease in trade means a decrease in trade with other nations creating a depression in the global circular flow of income.
Diversified industry. Without protection there is an unbalanced economy as a result of excessive specialisation which in turn leads to over-dependence of a country on other countries. This is dangerous politically and economically. Protectionism promotes manufacturing internally pushing nations to become more self sufficient in all industries.
Cyclical unemployment. The imposition of tariffs and other duties helps expand employment and incomes. Tariffs restricts certain imports so that money is saved in the domestic economy which will be spent upon the purchase of the products of protected home industries. As these industries expand so does employment and then the economy.