there is overlap in some of the reasons eg 1 & 2.
I never found some of the stated reasons particularly convincing, (ie. WMDs, link to terrorism) although I never thoroughly discounted them either. (that Saddam tried to acquire wmds in the past is certainly no secret, building a nuclear reactor in a country with huge oil reserves, using chemical weapons during the war with Iran, and on the Kurds) whether Iraq still had them is another story, although having read of Saddams fascination of weapons Im not sure that he had given up trying to acquire them as after all he was a survivor and the best way to remain in power is to have wmds.
In his interview with Dan Rather he stated that his one regret was not having nuclear weapons when he invaded Kuwait.

I would say that my primary reasons for not being against the war, are humanitarian, Iraqi people will be free from the killing and torture that has gone on for the past 30 years.

probably the most convincing reason that the US has gone to war is the idea that by setting up a democratic state in the middle east will lead to further change in the region - ie. the US new world order - (its certainly risky and) whether this really will remains to be seen. But one can look at the asian countries and its quite clear that the post war growth in Japan set an example for South Korea, Thailand and other emerging asian economies. a Pivotal issue is also the settlement of the Israeli-Palestinian conflict - as long as that continues it will cause uncertainty in the region and further inflame anti-western feelings.

I dont believe that Iran is next, there is already popular pressure for reform in Iran, as far as North Korea - the threat of nuclear retaliation will prevent any US attack - probably what will happen would be an attempt to blockade NK. NK is close to economic collapse anyway.