Iraq: making us weaker

Taylor Marsh runs an article by Charles V. Pena, who discusses some numbers concerning troop levels, rotations, deployments, etc.:

For a professional volunteer military force to be able to retain soldiers over time, the rule of thumb for active duty units is a 3:1 rotation ratio (meaning three units are needed to keep one unit fielded). So keeping 135,000 troops in Iraq requires an additional 270,000 for rotation or a total of 405,000 soldiers. This number is precariously close to the total size of the active duty Army, about 500,000 troops. Moreover, the U.S. Army has another 64,000 troops deployed elsewhere overseas that requires a total of 192,000 troops to sustain it. So when you do the math, the Army is about 100,000 soldiers shy of being able to keep up the current deployments.

[snip]

According to conventional wisdom, the force ratio required for imposing stability and security is 20 troops per 1,000 inhabitants, which is what the British – often acknowledged as the most experienced practitioners of such operations – deployed for more than a decade in Malaysia and more than 25 years in Northern Ireland. With a population of nearly 25 million people, to meet the same standard in Iraq would require a force of 500,000 troops for perhaps a decade or longer.

This is the clearest explanation I've seen so far about how this occupation is weakening the United States military's capacity to respond to other threats (to say nothing of the occupation's immorality, stupidity, and counterproductivity.) I wonder if someone from the Bush administration will respond to this. Or maybe Joe Lieberman can offer an explanation as to how this is all a good idea.