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Advocates of entirely open borders tend to advance two types of arguments. The first is economic. Opening all borders would make the world instantly richer. Some believe that it could double the world’s GDP. That is because workers become more productive as they move from a poor country to a rich one. They join a labour market with ample capital, efficient firms and a predictable legal system. If they are service workers, they will find richer and better-paying clients. By some estimates, more than two-thirds of a person’s overall wealth is determined by where they live and work.
The second argument for open borders is a moral one. Where someone is born is entirely a matter of chance, so there is no moral justification for compelling people to stay in a poor country. By the same token, those lucky enough to have been born in rich countries have no right to exclude others from their good fortune. Opponents of open borders are not convinced by either of those arguments. Even if the world as a whole were to grow richer thanks to open borders, they say, poorer people in the migrants’ destination countries would suffer. The new arrivals would depress their wages and compete with them for resources such as social housing and unemployment benefits. The welfare states that Western democracies have painstakingly built over the past few decades would collapse under the task of absorbing millions of people ill-suited to local labour markets. Cultural conflicts between natives and immigrants would before long cause violent clashes, threatening social stability.
The Economist