A popular argument against free trade is that the logic of trade requires identical (or at least similar) rules/institutions between the trading parties. Dani Rodrick recently made this argument, and you can see Don Boudreaux’s response here. There is absolutely nothing in the logic or argument for free trade that necessitates similar institutions between the partners. Only one thing is required: both parties benefit.
However, for both parties to benefit from trade, they must inherently be different from each other. If the two were identical, then no trade would ever occur. Diversity in tastes, in endowments, in incomes, even in rules, are desirable and, to differing degrees, necessary. The idea that trading partners must be similar to one another, including in their belief structures, undermines the logic of trade.
Moving from the individual level to the national level, institutional diversity helps show actual costs and benefits of various institutions. For example, if the whole world were as protectionist as Red China in the 1950’s, no one would know what a horrible scheme that is as the whole world would have looked like massive starvation. Fortunately, the Chinese realized their mistake and have become rapidly more open-trade, thus leading to their huge economic gains lately, but it was the fact that institutional diversity existed that such folly was understood. If a given national government decides not to allow peaceful trading between their citizens and another group of citizens, then their citizens are harmed and the true costs of their institutions, as well as their true benefits, are not known.
Diversity is a necessary ingredient of trade.