ABOUT THIS time six years ago, I was writing thousands of impassioned words in favor of the U.S. invasion of Iraq, and casting flippant aspersions on the patriotism of anyone who might be having second thoughts. I had an overwhelming number of intelligent people on my side, not to mention most of the U.S. congress from both parties, the president, and virtually everyone I knew in rural Texas. We were convinced that Saddam Hussein’s Iraq was, in the words of the joint congressional resolution, “a continuing threat to the national security of the United States and international peace and security.” In spite of stern warnings about treacherous foreign entanglements from Vietnam veterans and George Washington, it was a bad time to be, as Iraq hawks liked to put it with such swagger, “on the wrong side of history.”

As American troops finish pulling out of Iraq's cities this week, we have, as a country, a final moment to reflect on the mission that we all gave our armed forces in early 2003. Many of us long ago admitted we were wrong about the war; others, pained by the depressing feeling of writing off such a colossal expenditure as misguided, choose to focus on whatever bright sides of the result can be found. For this one last time, I could probably get away with saying I was a stupid college freshman when the whole thing started, and can’t be entirely blamed for my uninformed support. But it weighs on me even so. The best I can do now is to take the painful lessons of the past six years and hope to never make the same misjudgments again.

The facts, which no one was particularly interested in during the winter of 2002, are now soberingly clear. To be sure, Saddam Hussein was a despicable human being who repeatedly defied the United Nations and who the entire world—including the naysaying French and Germans—believed to be in possession of dangerous weapons. Even so, as former Bush official Richard Haass argues in his new book, invading Iraq was a choice. Hussein could have been contained, and U.S. interests could have been pressed in other ways, and we knew it. In fact, it now looks as if no one cared. As Bush administration officials have widely acknowledged, there was no conversation about whether or not to go to war (it was always assumed we would), no plan for dealing with Iraq’s complex tribal structures, and little interest in waiting for more information. The centerpiece of Colin Powell’s infamous 2003 presentation to the U.N., linking Saddam Hussein with al Qaeda, was the false confession of Ibn al-Shaykh al-Libi, who made up the story when we handed him over to the Egyptian secret police to be tortured in ways our laws would never allow.

The hasty and incurious insistence on war, not to mention the ways the Bush administration trampled American law and basic human decency underfoot, is shocking now that we know the details in full. They claim they were doing what it took to protect the United States, and, for a good while, we were content with that explanation. Even in my retrospective anger, it’s difficult to judge too harshly men and women who were faced with the enormous cloud of fear hanging over our nation in those years between September 11 and the beginning of the Iraq invasion. It’s easy to forget how that felt. But the place we ended up as a country is so embarrassing, so counterproductive, and so unnacceptable that we should all be wondering where we went wrong, and how we’ll approach the next situation—and it most certainly will come—where we must consider difficult foreign policy options. Presidents act on our behalf, and we are absolutely culpable for their actions. Personally, I’ve narrowed it down to this: beware of acting out of either fear or the desire for revenge.

Most of the grave transgressions of our national values were broadly justified by necessity: we have no other choice. We had no choice but to dangerously expand executive power; no choice but to ignore our international commitments; no choice but to turn the C.I.A. into a torture machine; and no choice but to launch an unprovoked invasion. Rattling the list off now, it’s easy to see that of course we had other choices. But blurred and prodded by fear, those choices seemed murkier than they were. There’s even credible speculation that President Bush and Dick Cheney were powerfully affected by reviewing raw intelligence reports that really, from an intelligence point of view, they had no business looking at before they’d been properly analyzed. Some of our national fear was genuine, some of it was manufactured, but either way, the result was to rush our judgment in way that the facts never warranted.

Hand-in-hand with that national sense of dread was our feeling—expressed perfectly in Toby Keith’s popular song about “putting a boot in their ass” and in Darrell Worley’s about “looking for a fight”—that someone had to pay for what happened on September 11. I’ll confess, in 2003, I didn’t really care whether it was Osama bin Laden, Saddam Hussein, or Ayatollah Khomeini. But turning our revenge impulse into a blank check for war wherever it could be found was incredibly simple-minded and short-sighted. Is our bloodthirst satisfied now that nearly 100,000 Iraqis have died in our conquest, not to mention over 4,000 of our own soldiers? Are we happy now that so many people in the Middle East who previously had no conflict with us now hold us responsible for the disappearance, torture, and death of their innocent friends and family members?

Those realities are difficult to swallow, and I feel partially to blame for my participation, however miniscule and irrelevant it might have been. But there is reason to hope that the next stage will hold renewal for Iraq. They’re happy to be rid of Saddam Hussein, and equally happy to be rid of the United States. In barely five months in office, on the basis of his biography alone, our new president has changed the world’s mind about America. (I recently met more than a few people in the Middle East who want to believe America is their friend just because Barack Obama’s middle name is “Hussein.”) With the last few dark years behind us, maybe the new Iraq will, after all, be our stepping stone to friendship with the Muslim world. But the heartbreaking part is that we could have earned it in any number of far less bloody ways, if only we’d stopped long enough to count the cost.

Discuss the Iraq pullout here.

Correction, July 6, 2009: This article originally stated that U.S. troops were withdrawing from Iraq, and did not specify that troops will only be leaving the country's cities. It has been updated.