> The argument for the war in Iraq was not that Hussein was involved in 9/11.
Direct links of the Hussein regime to al-Qaeda was prominent as justification for the war.
> The argument was that Hussein had WMD (reasonable assumption given that the US had given him a bunch of chemical weapons and he had used them against his own people), and that intelligence said he was going to attack next. It was a "preemptive" war.
This is false. While claims about WMD (many of which were false, and known to the US to be false at the time they were made -- as pointed out in the same UN session where Powell made his famous presentation, several of the specific claims in that presentation had been researched and debunked by UN weapons inspectors prior to that time) were made, there was no claim of specific intelligence of a planned attack, but just the specter that if Hussein acquired WMDs as the Administration claimed he was actively seeking to do and near doing, then he might either use them directly against the US or its allies or transfer them to terrorists who might do so. It was not a preemptive war as that term is generally used, it was an example of a broadening of that concept beyond the traditional notion of imminent threat to a speculative and future threat, which might best be described as "preventive war" (if one felt the need to distinguish it from any other instance of simple aggressive war, which it unmistakably was.)
> However, hand waving that everyone in America was so stupid as to believe Hussein was behind 9/11 really undermines your other points.
The majority of Americans did believe that [0], and that belief persisted at significant, though reduced, levels several years later [1][2]. I'm not sure how accurately relating facts undermines the grandparent comment's other points.
[0] http://usatoday30.usatoday.com/news/washington/2003-09-06-po...
[1] http://www.cnn.com/2006/POLITICS/09/06/iraq.poll/index.html
[2] http://www.cbsnews.com/news/polls-truth-sometimes-at-odds/