We are there to try and bring stability to an area we depend on for oil. ITs that simple. Iraq was the easiest target. they were practically wiped out militarily before, we thought we could get the world behind us, Saddam is a bad man no denying that, and we could loosly link him to terrorism.
IF, and a BIG IF this war was about terrorism, well you don't invade a country and set up shop to fight terrorism. small infiltrating groups are what you need, and if you we're going to invade a country, try beefing things up in afghanistan again, or kuwait, or saudi arabia or Iran, more terrorists from there than iraq. Its a weak argument.
For every "terrorist" we've killed over there instead here, the US has drove 10 to an extremist group hell bent on killing americans. Although they aren't stupid, and will train, and look for weaknesses and then attack again. This religion thing has been going on for 2000 years, it ain't stoppin now.
If this war was about Saddam being a bad man, we could have had him killed and be done with it, but that would have plummeted the region into more unstability, thus cutting off our supply of oil once again.