It's balance of forces. The population didn't rise forever, it won't fall forever. Even at 50% replacement that takes decades to manifest. The current conditions (overcrowding and a feeling of 'stress' in the population) are temporary. And besides, what problem is it if there's half as many people in the country 50 years from now? It's more space for everyone else. The Black Death is a historic example; living standards improved drastically after the population fell a bit.