I agree pop growth is an issue... But asking the pop to drop by two thirds is out of bounds. You cannot get that drop without natural decline over many generations or some kind of dreadful calamity. Natural decrease will happen but over generations, with the expected economic consequences of fewer people contributing to an economy. Maybe Japan can show the way, but so far, they are still basing their economy on growth which is incongruous with their demographics and it hasn't worked out too well and seems to be headed towards deterioration, barring external changes (like importing young people).