All things considered, we entered Iraq for all the wrong reasons. It really had nothing to do with WMD's.
Bush wanted an easy victory in the Middle East and to democratize a country there by force. By doing so, browbeat neighboring states into further democratization. Iraq was the best target. They pissed off any neighbors who would be willing to support them. The world already aligned against Saddam once. His military forces were crap. We were already in the area. NOBODY would miss Saddam's removal. Least of all the Iraqis.
By democratizing Iraq, we would draw in wannabe jihadis to the area to be met with military force. It would draw away potential attacks to Europe and the US. Iraq being easier for a Saudi, Syrian or Jordanian wannabe bomber to go to than the West. Draw them to Iraq, annhilate them and show the world how ruthless these Islamicists are to fellow Muslim civilians.
The problem was, it was done too much on the cheap. We believed far too much of our own propaganda bullshit as to what would be needed for occupation and we got lazy when it came time to providing the necessary level of commitment of forces.
That being said, Saddam had it coming. He deserved his fate. The country has toned down quite a bit since 2003-2004.
Iraqis are really taking to democracy a lot better than expected. The civil war everyone was expecting between the Kurds, Shia and Sunni has not materialized. If anything Al Queda's attempts to spark one has actually brought Iraqis closer together. They are actually looking at political solutions to the ethnic divisions. Something one does when they want to be democratic.
You can even say that the war helped spark the Arab Spring. Once it was seen that the West would be willing to support Arab democracies over longstanding cronies. You had an actual example of an Arab country with a democratic leadership, it undermined the sad myths that Arabs just weren't ready for democracy.