No matter how much I try I can’t get my head around the common leftist (and libertarian) delusion that national borders should be abolished and completely free movement of people allowed across the world.

At the risk of infantilising the argument – though maybe that’s what it takes for some to comprehend the issues involved and their implications – nation-states are like houses: houses have walls and doors, not just to protect residents from the elements, but also to give them control as to who they let in and who they refuse.