While this is a somewhat provocative defense of war, I think it falls well short of an actual justification for attack.
First, a lot of attention was directed at the sanctions problem over the past decade. Many people favored "smart sanctions" that would minimize the harm to innocents and maximize the containment value (deny military equipment, etc.). Essentially, US policy towards the Soviet Union and its satellites was governed by "smart sanctions" through much of the 1970s detente era. Granted, the Soviet economy was sufficiently large and powerful to build weapons indigenously, but Saddam Hussein's Iraq would have needed trade. It would have been relatively easy to allow food, medicine and even consumer goods, even as weapons and arms-related good were banned.
Second, while 5000 American troops were tied up in Saudi Arabia, about 120,000 are now in Iraq -- and will be there for many years under current Pentagon planning. The war is also diverting important resources from the war on terror -- as I keep mentioning.
The US expended diplomatic capital on Iraq because it considered Iraq one of the worst rogue states in the world, long before 9/11. Even after Iraq was relatively easily defeated, had its weapons programs dismantled, and suffered more than a decade of sanctions, some people still viewed it as part of an "axis of evil." This was threat inflation, pure and simple, and was distracting because the US made it so.
Finally, there is very little reason to believe Iraq would have been a major regional threat. Many international relations theorists viewed Iraq's past "aggression" as mostly defensive. As John Mearsheimer and Steve Walt pointed out in their Foreign Policy article from January/February 2003, Iraq may have had reasonable (and defensive) reasons for attacking both Kuwait and Iran. Kuwait was exceeding OPEC oil quotas and wasn't negotiating a solution to that or to debts related to the long Iran-Iraq war. Iran had been stirring up dissent within Iraq, attempted to kill Saddam, and had even gained territorial concessions.There is also pretty good evidence that deterrence failed in Kuwait because US Ambassador April Glaspie said the following at a July 25, 1990 meeting with Saddam Hussein:
We have no opinion on your Arab - Arab conflicts, such as your dispute with Kuwait. Secretary (of State James) Baker has directed me to emphasize the instruction, first given to Iraq in the 1960's, that the Kuwait issue is not associated with America. (Saddam smiles)As Mearsheimer and Walt wrote, "The U.S. State Department then reinforced this message by declaring that Washington had 'no special defense or security commitments to Kuwait.'”
I'm not trying to defend Iraq's past behavior, and Saddam was certainly a very bad man, but that does not mean the US should default to war to attack and topple bad regimes headed by horrible tyrants. President Bush himself opposed war in Rwanda, even when asked during the 2000 campaign if it would have been worth saving 600,000 lives.
Since 9/11, the US has focused tremendous attention on the problems of transnational terrorism and weapons of mass destruction. The war in Iraq did very little to address either of those problems, ticked off key American allies, diverted resources, angered millions of Muslims (thus, potentially increasing the pool of terrorists), and undercut the rule of international law (necessary for fighting terror and criminalizing proliferation of WMD).
The above is not an especially thorough critique of the Yglesias case. For more on Iraq specifically, I would recommend reading the writings of David Cortright, George Lopez, Eric Herring, and Marc Lynch. All these scholars worked on Iraq sanctions and threats for many years before the US went to war in March 2003. None liked the sanctions regime and all saw legitimate alternative policies that were not pursued.
The alternative policy to the WMD/al Qaeda justification for war was not simply a "better case" for attack.