The question in the title is perhaps the most important question we confront, and will continue to confront in the years ahead. I discuss my take in this paper.
Many economists tend to be global-egalitarians and believe borders have little significance in evaluations of justice and equity. From this perspective, policies must focus on enhancing income opportunities for the global poor. Political systems, however, are organized around nation states, and create a bias towards domestic-egalitarianism.
How significant is the tension between these two perspectives? Consider the China "trade shock." Expanding trade with China has aggravated inequality in the United States, while ameliorating global inequality. This is the consequence of the fact that the bulk of global inequality is accounted for by income differences across countries rather than within countries.
But the China shock is receding and other low-income countries are unlikely to replicate China’s export-oriented industrialization experience. So perhaps the tension is going away?
Not so fast. The tension is even greater somewhere else: Relaxing restrictions on cross-border labor mobility would have an even stronger positive effect on global inequality, at the cost of adverse effects at the lower end of labor markets in rich economies. On the other hand, international labor mobility has some advantages compared to further liberalizing international trade in goods.
I discuss these issues and more here.