1. There was a massive worldwide movement opposed to the invasion in Iraq. There were record-breaking demonstrations in all the capitols of the free world. Nearly all of the pacifists fears for and objections to the war look in hindsight to be much closer to the truth than anything that the people who planned the war were saying.
2. Many people who opposed the war, and some who provided grudging support for it had serious doubts about the justifications provided, including pretty comprehensive doubts about the intelligence that provided said justification.
3. The findings of Hans Blix and the UN inspectors in Iraq before the invasion, that there were no detectable programs to develop and produce weapons of mass destruction in Iraq, have been shown to be accurate.
4. The fears many expressed before the war of high casualties and street-to-street fighting have turned out to be valid. People just thought the ugly urban warfare would start earlier, during the invasion.
5. No matter how you judge it, people in Iraq are not materially better off than they were before the war. They now have more freedom of speech, but they can be shut down for being too critical of the occupation forces or the government. They no longer have to fear arbitrarily meted out brutality from the state, but they now have to fear brutality meted out by religious fanatics, remnants of the Baathist regime, criminals, and sometimes, the United States Armed Forces. The main change for those on the receiving end of the current violence is that the Hussein regime was more scrupulous about maintaining a paper trail.
6. We've spent something like $166 billion on Iraq and looking to spend 26 billion more over the next year or so, with no end in sight. You can do a lot of good in the world with a quarter trillion dollars -- I honestly don't think we're getting our money's worth.
Pacifists get a lot of shit about being impractical. "Some people only understand force," "What would have happened if we hadn't fought Hitler?" "Rwanda?" "Bosnia?" "Kosovo?" "Al Qaeda?" "Kuwait?" Those are hard questions to answer as a pacifist. My best answer is this: In hindsight, we know where and when those problems all started, and in most cases, we the people, and our government, were guilty of standing by, doing nothing when there was still a chance to head the problem off. In some cases we actually helped create the problem -- we supported Iraq in the Iran/Iraq war and sold Saddam Hussein weapons. We funded the Mujahedin in Afghanistan in their war to expell the Russians. We train officers in our War College that go back to their home countries and use their expertise to murder and torture civilians.
No one really likes War except sociopaths addicted the adrenaline rush, and those who stand to benefit politically or financially. There are over 10,000 families in the United States and many times more in Iraq and Afghanistan whose lives have been devastated by the war in Iraq. Killing people into freedom hasn't really worked yet.
My brother once had a voice class in college. One day he was singing for his professor, and the prof stopped him and said, "you've just sang it in exactly the same wrong way four times. Try singing it in a different wrong way." The point being that if you keep doing the wrong thing, it never hurts to try something different, because the worst thing that can happen is that you'll be wrong again.
The fact is that the impracticality of pacifism has never been proven. If you study on the issue (and I'll recommend some links below) pacifism has had some small beneficial victories. War, no matter the outcome, is pretty much and end to end clusterfuck. War is the result of greed, tribalism, lunatic ideological certainty, a lack of imagination, and a lack of patience. War destroys things that we just have to build again. Wars engenders the hatred and anger that become the seeds of further wars.
What if we tried peace? What would happen if we became students of the ample history of the causes of war, and were vigilant in addressing the causes with positive, non-violent action? What if we engaged positively with governments all over the world to try and engender mutual trust, and enlarge and reinforce the common values and goals we share? What if we looked at the injustice and opression that fuels support for insurgencies and tried to address them?
It might not always work, but for fuck's sake, war doesn't work either. To quote my favorite hippy John Lennon, "all we're saying is give peace a chance."
The American Friends Service Committee was started by people from the Religious Society of Friends, but has evolved into an organization encompassing both Peace Churches and secular pacifism.
The Paradox of War and Pacifism This is actually a scholarly treatment of pacifism in the context of Christian faith, and I find it's justification for war on the basis of the Bible sophistic and specious - a topic for another time. But it presents a lot of good information about the history of war in the western, Christian tradition.
The Pacifism of Bertrand Russell
Pacifism in Buddhism, which includes an interesting article about the Dalai Lama in the New York Times that implied he would support violent countermeasures to terrorism, and the response from the Dalai Lama's representative.
The Pacifism of Islam
Teaching Peace, from our friends to the north.
The Quakers, OG Pacifistas, AKA Religious Society of Friends