The Iraqis are weary unto death of the antics of Saddam Hussein, who represents a minority within Iraq. Sensibly, perhaps Iraq should be three countries, as there are three major (and mutually hostile) ethnic groups, the Kurds, the Sunni, and the Shi'ites, all Muslim, but also at each other's throats when there is nothing else to occupy their time and thoughts.
Iran is a different kettle of fish entirely, as the people of that country, while Muslim, are also Farsi, who speak a different language, have an entirely different history, and have at least some semblence of representative government based on a legitimate code of law in their past, which is something that has not been known in Iraq since about the time of Hammurabi. Given that there were a change of regime in Iraq, the Iranians would undertake their own election quickly enough. Such a chain of events may not bode well for the Saudis at all.
Once Saddam is gone, I just cannot see a down side on the long term.
But in the short term, every pro-pal terrorist will be looking for revenge, and every tin pot dictator will be trying to figure out how to strike at us without it being traced back to its source.
It's not that I flat-out think attacking Iraq is wrong, I just want to know that it will be worth the treasure and blood we will have to expend.