Did it make sense to go to war in Iraq? The original justifications for the war related to US national security -- Saddam Hussein was a threat to the US due to his weapons of mass destruction, and there was a connection between Iraq and the 9/11 terrorists. Having abandoned those justifications, the Bush administration is now saying the war was worthwhile due to the benefits it will bring to the people of Iraq.
Assume for the sake that argument that the war has resulted in a net benefit to the Iraqi people (which is by no means clear). Even so, one must still do a cost/benefit analysis to determine if the war was worthwhile. Before this thing is through, the cost of the war will be 100's of billions of dollars, with the loss of thousands of lives (both American and Iraqi). That much money could have done a world of good if spent on unmet needs at home, such as education and health care -- and all without any loss of life.
Do the benefits of the war to the Iraqis exceed the forgone benefits at home? Almost certainly not. Of course, the whole comparison between benefits in Iraq and benefits at home may not make sense to Republicans. They may take the position that the government shouldn't be spending any money at all on unmet needs at home. But that raises the question -- why is is OK to help the Iraqi people, but not to help people in the US?
Normally, of course, you would not justify a war by comparing its benefits with the forgone opportunities at home. But most wars involve US security. Having conceded that the Iraq war didn't involve US security, the Bush administration is outside the normal calculus for wars. It must justify this war on a cost/benefit basis, but apparently could not do so.