One quick look at the trouble we face with North Korea actually strengthens the case for military action in Iraq.
Here are the problems with face with N. Korea. They are even more notorious than Iraq about breaking deals. They already possess Nukes, if we leave them be, eventually, these nukes, like every other armament NK makes, will end up being sold to the highest bidder. Should we take military action now, 100's of Thousands, perhaps millions in both NK and SK will die.
Do we want to be in a similar fix with Iraq in 5 years? Take out Saddam now, then lets deal with NK and their nukes (hopefull, China will see it's in their best interest to do so.