A population problem?

As the US population surpasses 300,000,000, Richard Posner argues that overpopulation, despite the hysteria of doomsday predictions in the past, is a legitimate cause for concern.  Gary Becker disagrees.  One particularly provocative remark from the comments (not from either Posner or Becker) struck me:

The operative word is sustainability. If there are three-to-five billion people in the world who are dependent on aid from developed nations to live, and that past aid has not proven the ability to make these societies self-sufficient, is it ethical to continue the aid and watch the populations balloon, knowing that the aid is finite?

Rob