A nation is in a sense an extended family. Members feel some duty to look out for each other beyond simple self interest. This breaks down when too many foreign

A nation is in a sense an extended family. Members feel some duty to look out for each other beyond simple self interest. This breaks down when too many foreigners crash the party. They don't have skin in the game or ties to the soil. They will leave at the first sign of serious trouble. They will be less inclined to think about the long term.