As one who thinks pacifism "works," I've tried to think how I would argue with an Iraqi who is convinced that blowing himself up (and perhaps taking out some coalition troops or police recruits) is the best thing he can do to get the US out of his country. (Obviously just saying that he might kill innocent people won't persuade such a person; he'd sneer and point out that his enemies do it all the time.)
I still don't know enough about the situation to give a plausible recommendation for alternative, peaceful strategies--in contrast, I am quite confident that the official US objectives, such as reducing terrorist attacks against Americans, would have been better achieved by not engaging in massive violence against Iraqis--but one obvious consideration is this: If you blow yourself up in a suicide attack, you no longer contribute to your cause. But if you stay alive, you can contribute to your cause for the rest of your natural life (unless you get killed by your enemies, of course), and even perhaps bring up several children who will be predisposed to your worldview.
Yes, staging a sit-in or talking to an Amnesty International reporter won't do much, but you get tens of thousands of chances to do such "inconsequential" things if you stay alive. If you blow yourself up, thinking that's the best use of your life, you don't get to reevaluate that decision later on.