No calculus, however tortured, can justify the costs of the Iraq war. Put aside the steep human costs, both for Americans and Iraqis—which are well-documented and are alone enough to tip the scales toward "not worth it"—and examine the strategic costs.
Removing Saddam Hussein from Iraq ousted one of the main forces balancing Iranian influence in the Middle East. The resulting democracy is fragile at best. Iraq remains beset by violence.
The war consumed the attention of U.S. policymakers, diluting what should have been a narrower, but much more intense, focus on al-Qaida proper. Remember, the Bush administration gave up on the search for Osama bin Laden.
Consumed with the chaos in Iraq, American policymakers took their eyes off the war in Afghanistan—where the 9/11 attacks were hatched—allowing the situation to fester into a much deeper problem. The U.S. diverted surveillance assets from Afghanistan to Iraq in 2002, and troop commitments for Iraq left the effort in Afghanistan desperately undermanned until 2009.
Fighting in Iraq wore down the U.S. military. Defense investments geared toward winning an extended occupation in the Middle East (rightly) took precedence over investments in future capabilities, pre-empting investments in new, high-end systems.
So even while base defense spending grew about 80 percent over the last decade, with more than $1 trillion in direct war spending added on top, the Defense Department today faces a dual challenge of equipment replacement, maintenance, and modernization,all while budgets decline.
More broadly, the Iraq war fed global perceptions of U.S. decline—superpowers are supposed to be competent above all. And it contributed to additional factors feeding an (incorrect) sense of U.S. decline internationally, such as a lack of domestic investment and national growing debt. Finally, the conduct of the war, fought by a minority of Americans and paid for on credit, widened the disconnect between citizens and the war being waged on their behalf.
Some have argued that only historians can truly determine whether the results of the Iraq war justified the costs. Many say it's too early to tell.
It's not too early—not by a long shot. Wisdom, and the process of learning from history starts by calling things by their right name. Iraq was the greatest strategic blunder in American history, an "un-forced error" of monumental proportions. We should draw lessons from there.