How do you think these developed nations will fill vacancies in their nations and get cheap labor if the population of these developing nations is reduced?
What is happening in those developed nations is that the native populations of the countries are decreasing, while they are importing labor force from foreigner countries, especially from third world countries from Asia and Africa. The Europe like we have known along the centuries and decades doesn't exist anymore. Nowadays globalization and miscegenation have taken place with total strength and it seems the whole world will be prettt default, without any different characteristics among the people from different regions, countries and continents. If it's good or bad will depend on the point of view of each of us. The question is if such changes are functional or disfunctional for the respective societies where changes are taking place.
This is the beauty of having a steady growth of population, the government is able to send people abroad to work without worrying about the shortage of manpower. The country is able to make a profit from these laborers through taxes.
The population needs to be literate in order to see them as a potential help. So country with a booming population should not neglect the literacy of its constituents.