Why Do We Need to Maintain a Certain Level of Population?

The global total fertility rate needs to be at least two point one children, poor women to day. What happens when the total fertility rate decreases below that level and we don't have enough people? A plumbeting population leads to rising labor shortages. Less workers means less tax revenue for safety net programmes like pensions and health care. And so is your thesis that actually to vitalize world economies, to revitalizeand actually entire nations, we need to have more kids?