We did not go into Iraq for glory, or for conquest, or for monetary gain. We went in to stop someone from acquiring nuclear weapons, at which point he would have been able to threaten a large portion of the Middle East (including Israel) and also a fair chunk of Europe. We also went in to depose a man who was torturing and murdering his population.
Right now Iran is ramping up to get nuclear weapons. Is your position that we should WAIT until they have a nuclear weapon and USE IT?
I take dispute with your claim that we went in to stop Saddam acquiring nuclear weapons. My understanding was that we believed he already had "weapons of mass destruction". Hence the thorough search and subsequent recriminations when it came up empty. I also believe that an Islamic Iraq is more of a threat to Middle Eastern peace than the previous version run by a secular dictator.
As for Iran, I consider any country with a radical Islamic leadership and nuclear weaponry to be a clear danger which may well merit a pre-emptive strike. However, we must be absolutely certain that it has the weapon(s), and not merely suspect it through half-baked intelligence. It's not sufficient simply to have "good intentions" when starting a war. Most errors are made sincerely and with the belief that the right thing is being done.