Peter Beinart makes  an odd argument:
Part of the rationale for giving people who got Iraq wrong last time the chance to explain why this intervention is different is that they may be right. Supporting the Iraq invasion was an unusually big mistake, but sooner or later, almost everyone who offers opinions about war makes mistakes. Ted Kennedy opposed overthrowing Manuel Noriega. Colin Powell opposed the Gulf War, as did most Democrats in Congress. Jimmy Carter thought it such a bad idea that he urged other nations to reject authorization for force at the UN. Michael Moore opposed NATO’s military intervention in Kosovo.
This list is revealing, but not in the way Beinart intends. Beinart takes for granted that pretty much every other modern military intervention before the invasion of Iraq was the right thing to do, and so assumes opponents were badly mistaken. There are two rather glaring problems with this. The first is that it is not remotely obvious to anyone except consistently hawkish interventionists that invading Panama and bombing Serbia were the right things to do. Insofar as both of them helped pave the way for the later, more costly illegal war in Iraq, they did real harm to the U.S. Because neither was actually necessary for U.S. security, it was wrong for the U.S. to resort to force in these countries. Kosovo arguably provided a pretext for later Russian interference in its near abroad, and the war in 1999 demonstrated that the U.S. and its allies would trample on international law when it suited them to do so. The farther we get from the debates of 1990-91, the harder it is to fault skeptics for their caution and reluctance. While it may have been justifiable and legal to expel Iraqi forces from Kuwait, it is also the case that the war embarked the U.S. on a course of twenty years of sanctioning, bombing, and eventually invading the country. As the current debate shows, the U.S. is still in danger of being pulled back in. The costs of our Iraq policy over the last two decades have been enormous, which makes it fair to wonder if the skeptics in the early ’90s deserve a lot more credit for their caution than they usually receive.
More important, Beinart treats the Iraq war hawks’ “mistake” (colossal blunder would be more accurate) as if it were the same as the “mistakes” of opponents of previous wars, but there is almost no sense in comparing them. Interventionists routinely warn about the “costs of inaction,” but the Iraq war and the Libyan war (which Beinart also supported) show us the measurable and sometimes very steep costs of doing what they advise. The Iraq war in particular was the greatest foreign policy blunder in a generation. Surely it must count against someone more to get a major policy decision horribly wrong than to be on the “wrong” side of a more debatable and relatively minor decision.
Then there is the refusal of many Iraq war hawks to own up to what they got wrong. Many of the loudest advocates for action in Iraq today have remained either oblivious to the consequences of the policies they supported, or they actively deny responsibility for those consequences. Unlike Beinart, many Iraq war hawks have never admitted significant error. At most, they have usually retreated to the last defense of the ideologue: “The policy was sound, and it was just the execution that failed.” They haven’t repudiated their old views, and they have never taken responsibility for the failure of the policy they supported. Indeed, so delusional are some of them that they insist that the Iraq war had been “won” right up until U.S. forces left. So one of the reasons that it is appropriate to pay little or no attention to the predictably hawkish recommendations of Iraq war hawks is that they have proven to be impervious to evidence that their previous assumptions were profoundly wrong. It is impossible to take seriously arguments from people that willfully ignore their own past mistakes in analysis and judgment.
As long as Iraq war hawks pretend that recent events have somehow vindicated their old arguments, their arguments should be dismissed as the desperately self-serving claims that they are. Another reason to pay them no mind is that many of them are repeating similarly misleading arguments  and perpetuating false assumptions about the efficacy of hard power that led them to blunder as badly as they did twelve years ago. Having learned absolutely nothing from their failure, they have nothing to teach anyone else. They are free to say their piece, but it would be a waste of time and energy to pretend that they are saying anything worth listening to.