Is NumbersUSA making a fundamental miscalculation?

Here is a link to an interesting article on ILW.com, regarding the looming environmental and financial peril to be caused by immigration driven overpopulation.  This is a favorite bugbear of restrictionist groups founded or sponsored by John Tanton (like NumbersUSA).  This article takes a different view and argues that immigration to wealthier countries like the United States is good for the environment and will help prevent overpopulation. It is worth reading even if you don't agree.

http://www.ilw.com/articles/2009,0903-richman.shtm