DC anyone who denies that oil was a part of the equation is naïve . The whole purpose of Desert Storm 1990 was to prevent Hussein from taking control of the majority of the Gulf Oil.
Again ,in the 1990s there was a growing consensus (shared by Clinton and Gore amongst others ) that the sanction regime was a dead end. Subsequent events surrounding the violations of the UN 'Oil for Food 'program proved that assessment accurate . The sanction regime would continue to weaken and primarily US and GB would have to either take decisive action or withdraw.
But you are not quite correct about 9-11 ,or rather 9-11 and the subsequent attacks on the US by anthrax (still of undetermined origin ) .
The idea of terrorist with their hands on WMD is to this day a real threat. That created an urgency to resolving the deadlock .
It is a fact that Saddam was the only modern world leader who had used WMD in warfare both against foreign foes and domestic . It is also well documented his ties to terrorist organizations ;and subsequent discovery of Iraqi documents post-invasion have proven that his relationships with AQ were in the development stage throughout the later 1990s .
It is debatable I suppose if these factors justified an invasion.But to attribute the decision to a single reason is inacurate .