IMAGINE YOU are offered a job at triple your salary. But first you must pass through a locked door, and someone with the key won’t open it. You might be willing to pay them to let you through. Whether this is fair or not is beside the point. They have the key and you don’t. If you gave them a portion of the increase in your wages, you would both be better off.

This is not a bad analogy for global immigration policy. When migrants move from a poor country to a rich one, they typically make three to six times as much money as before (see our Special report in this issue). If everyone who wanted to migrate were allowed to do so, the world would by one estimate be twice as rich. Yet this vast gain cannot be realised, because most would-be migrants are forced to stay where they are. The door is locked, and voters in rich countries hold the key.