Yes the world is overpopulated. However a lot of developed societies based their framework for budgets on permanent growth, for example the idea that the young paying tax will always pay for the benefits of the elderly. However with the population rate decreasing, suddenly there is lots of older population expecting things like healthcare and pensions to be paid for them. With less and less young people to cover the cost in tax, there is a looming defecit which is very worrying to a lot of economists.