Stephen Walt makes the correct objection to the Iraq war:
For starters, Bush and the neoconservatives mistakenly believed preventive war was justified because Saddam was undeterrable. But Saddam was not suicidal, and if he had ever obtained WMDs, he could not have used them or given them to others without facing devastating retaliation. It was always an unnecessary war.
As Walt says, the hawks’ attempt to hide behind the “bad intelligence” excuse is just a “smokescreen” to distract us from the reality that the Bush administration’s policy of regime change and “preventive” war was indefensible folly regardless of what the intelligence showed. The obsession with “bad” intelligence now is the flip side of pro-war advocates’ fixation on the shoddy, cherry-picked intelligence back in 2002-03. Today they hide behind the former to evade responsibility for the disastrous war they supported, and they do this with the same enthusiasm they used the latter to bludgeon opponents of the invasion as “not serious.” Supporters endorsed obviously shoddy arguments for war because they wanted the U.S. to attack Iraq to topple its government. The desire for regime change came first, and the pretext for it came later.
“Preventive” war is always unnecessary, and there can be no justification for it. The idea that any state can attack another because of some threat that the latter might one day pose is contrary to just war theory and international law. In Iraq, there was nothing to be “prevented,” and the war created new security threats that would never have existed otherwise. It is often the case that a war fought to “prevent” a threat from developing may instead create the very thing it was intended to stop, or it may produce new and unexpected dangers. These are the main lessons from the Iraq war that almost all of our presidential candidates (and most of our other politicians) fail to grasp. Indeed, they don’t want to grasp them, because they would get in the way of future military action against the next regime. It doesn’t occur to many of them that there could be anything wrong with such a war. That is why almost all of them have no problem entertaining the idea of illegally attacking Iran to “prevent” its acquisition of nuclear weapons, and they do this despite the near-certainty that attacking Iran would lead to the very outcome it is supposed to “prevent.”