[Heartofsong83]

If managed properly, the US could hold a billion people. However, that would likely only be possible if the growth was natural and not immigrant-induced. Some immigration should be encouraged (mainly to replace emigrants), but not as a population growth mechanism.

[Dante3]

With that many people, this would be a nightmare society - traffic jams, people piled on top of one another, psychological problems, our historic and nature areas destroyed, etc. Many areas of the country simply do not have the water supply to support a community.

[Jedi Master Pikachu]

Natural increase should grow (how about outlawing abortion for all non-fatal-life-threatening reasons?), but natural increase and immigrants have been dual engines of growth throughout this nation's history. Work should be done on assimilation (both ways, the immigrants becoming Americans; the American natives acknowledging that Americans can come in more varieties than the European/African-descended ones (and Amerindians, statistically tiny)).

[Jedi Master Pikachu]

P.S. A billion Americans could help protect the United States from other countries. The country has the upper hand against China now largely because of technology and political instability; how about in a future is a stable and technologically advanced China?