It fulfills a social contract: the service you provide by being born is carrying your parents&#x27; genes.  There is a three-way transaction between citizen, child, and state.  This is a boon; it allows social contracts with long time horizons to be made.  Take away preference for native-born citizens over foreigners, and you remove the incentive for citizens to leave a country better than they found it.  This is not an absolute---limited naturalization, like we have, has not caused the world to fall down.  But there is an effect.