I think as long as your argument is based on "what-ifs," you'll never win it because nobody knows what if. Just a lot of hot air on both sides. "Violence will increase." "No, violence will decrease." Who the hell knows? But that argument serves the purposes of the war-mongering bastards who started the war in the first place. WTF do they care if violence increases or decreases? If they were so worried about violence in the first place, they wouldn't have invaded a country that posed absolutely no threat to them. BUT: they can play your game and justify the continuing occupation of Iraq and the continuing slaughter of its people by saying - - with just as much authority as you - - that violence will increase if they pull out now.
That is a bullshit argument. It is not the function of the U.S.A. to regulate the levels of violence inside any other sovereign country. If the Iraqis choose to have one helluva drag-down, knock-out, no-holds-barred civil war, that is their prerogative and their right. They will settle their affairs their own way without your "help" - - which, BTW, has already cost the lives of 600,000 Iraqis.
The invasion and occupation of Iraq was a flagrantly illegal violation of international law, it was wrong in every respect, and it has to stop NOW - - not because that's the way to decrease the internal violence there, but because it's the rightful and lawful course of action to take. The ONLY rightful and lawful course, as it happens.