You are missing a few points. But first you are right it's crass to not want to buy Iraqi their freedom cause we looking for a better price. Similarly it's crass to be overly concerned about museum artifacts, when Iraqis and American soldiers are dying- especially when get the story wrong and most of the stuff is returned anyhow. But I'm wandering.
First the price tag of a trillion dollars is misleading in numerous ways. It's similar the idea that going to the Moon would cost a trillion dollars.
If the same person were to say that the Iraq war is going cost 1 trillion dollars would also say that Kyoto agreements is going to cost a trillion dollars I would probably agree that they are using comparable metric. While the US could spend a trillion dollar freeing Iraqis, the rest world could spend a trillion dollars pretending they doing something about global warming.
And in this kind of loose metric I would agree that going the moon could cost about trillion, but actually I would prefer that we spend far more than one trillion dollars going to the Moon. And I think it's possible that we could spend a trillion dollar NOT going to the Moon and NOT going to Mars [I mean we have almost spent that much money not doing either of these things and at rate we are going will probably end up spending a trillion dollars before we actually start going to the Moon].

OK getting back to Iraq. I think we are going to actually make a profit in regards to Iraq- a big profit. Oh, yes this is crass, but I do think we will make similar profit from Iraq as we made a profit from defeating Germany and Japan. Not as much expenditure, but probably more profitable- gross profit will be less but profit to cost ratio being higher. Of course, I don't mean some war booty, or the Oil Companies, and the nonsense the Left whines about.
And I don't mean some "good" to the rest of the world [which also will be substantial] I mean profitable directly to the American people. Now, I can't prove this, but I think in the future it will be measurable. In simple terms, in WWII it was understood that war helped America because of increased industrial capacity, in the present Information Age it will be probably be "information related"- of course this probably sounds crazy. What is probably more realistic to most people was the potential loss of not doing anything about Iraq. What if we had simply lifted sanctions in regard to Iraq. Do you suppose we would even be considering the possiblity of putting sanctions on Iran? Could we in anyway be detering Iran from getting nukes and "wiping Israel off the map". If Iran is making nukes, wouldn't Saddam have a good case for allowing him to make WMD for defensive purposes?