Iran is "deeply rooted in Islamic Terrorism."  We all know what that means.  Evidence notwithstanding we don't need a reason to invade Iran.
1.  American people --> misinformed due to the media.  There was not a single news channel that was reporting a different perspective during the buildup to the war on Iraq.  Unfortunately, we are one of the most ill-informed industrial populations.  Our news industry is controlled by olgiarchs who have vested interests in the agri-business and petrolchemical industries.  You'd be surprised how much news is mis-reported or spun into something the US gov can use.
2.  Al Qaeda.  While Al Qaeda still exists, we will have every "reason" to invade any state.  OBL was allowed to leave Tora Bora.  Do you think that the US army, with all it's sophistication and technology and precise planning could have convientantly allowed a hole in their search networks?  I highly doubt that.  OBL is as cruical to the US economy as is the stock market.  Even the hint that OBL might be found can send stocks skyrocketing.  The fact that he might be in an area close to Iran is justification enough to invade.
3.  Hydrocarbon economy.  Combined wit the PACs and lobbying system and the dwindling of resources on our mainland, nearly every geopolitical event has to be viewed in terms of hydrocarbon acquistion.  Facts : US domestical oil production has been steadily decreasing since the 70s, 
http://www.hubbertpeak.com/us/ .  Natural gas production has also been declining steadily.  Compared to last year, we had to drill 6,400 new wells just to keep up with last year's production rates.  The year before it was only 5,000.  
http://www.hubbertpeak.com/gas/
4.  States that are "Deeply rooted in Islamic Terrorism" have an inordinate amount of natural resource wealth, things we need to continue our 12 mpg SUV driving and air conditioning on all night even though its only 75 degrees outside.   
http://www.aneki.com/gas.html http://www.infoplease.com/ipa/A0872964.html  Instead of beginning a large-scale push towards smallers, more economical cars, politicans rather pander to the american public by proclaiming that driving SUVs are one of the most american things you can do.  As a result of economic cars and other initiatives, Europe is closer to acheiving energy independance than we ever will be.  
5.  The Govnernment is adverse to the one thing that will bring relief to our lifestyle.  CHANGE.  Regardless of who is in office, it is the corporate interests that really determine american policy.  Perputating our energy intensive life-style instead of pushing for conservation, rationing, and simple common sense initatives bows before the altar of the status quo.