...but why would anyone ever want that?! If people are able to move freely, then each country should be able to apply tariffs to extract benefits from the econ

...but why would anyone ever want that?! If people are able to move freely, then each country should be able to apply tariffs to extract benefits from the economic gradients. If people can move freely, then that's the ideal. Institutions, governments, "nations" and companies that collapse because of the free movement of people deserve to collapse and should be left to due so. The should even be "helped" to collapse faster and harder, making sure they never rise again!