Make such mental experiment - imagine that all people decide not to have children and instead to invest saved resources in economy. Such generation will be VERY succesful until it becomes old. Then suddenly for "mysterious" reason the horrible crash will occur. All investments and savings will disapear and there will be plenty of old starving people dying like flies and begging foreigners to come and take over.
OK, how about this experiment. All the investments are made to produce and store food. No new food is produced but everyone has 50 years worth stored in the basement.
Old people need much more than very old food. What about electricity, water or heat in the winter for example? Can they store that for so long?