Sooner or later the masses of poor people are going to revolt and cut the throats of the rich people. It's like what happens in a nature's development, as on new land. The first pioneer organisms that colonize, like the first human pioneers, produce a lot of offspring. These first organisms are 'r'-selected. But as ecosystems and societies mature, the survival of the individual becomes more important than producing offspring.
Quality replaces quantity.
A boom and bust cycle in population sounds a little scary, especially with a world economy based on growth in size rather than quality. It's going to be painful either way. More is not better. You can't grow forever. You can try to keep the boom from going too high, because the higher the boom, the greater the bust.