This is a good thing. The carrying capacity of the planet is finite, and our large global population is largely responsible for the destruction of the environment and climate change. Further, the high standard of living of Americans places a significant burden on the resources used to sustain this lifestyle. 300k fewer Americans will have a much greater impact on the environment than 300k fewer people of any other country.

There's also the fact that the global population has to decrease at some point, à la Japan.