The idea that there were WMDs in development / ready to use at the drop of a hat was part of the motivation to go to war at the decision-maker level, but not the core reason, I think. It was more a "look out, he has a gun - rush him" kind of snow-job to get in there, with the idea that something could be found to justify that approach.

The bigger idea was a domino concept; that a remade Iraq would be a beacon of democracy in the Middle East, that all the other states would similarly switch over (one way or another) to democracy, Muslim fundamentalism would no longer be a threat, and the whole region would be a capitalist wonderland with oil. Sort of like 50s/60s communism in reverse. But it didn't quite work out.