If the Evil Neocons™ wanted to create the best pretense for war against Iraq, they could have done so with a fairly small conspiracy, something along these lines:
Assemble a team of Iraqi nationals to plant and explode a real WMD in NYC, killing thousands of civilians. Note: Planting explosives to bring down the WTC towers would not be very feasible due to complexity and security issues - previously a big bomb approach had been used and had failed to destroy a tower.
Once the Iraqi conspirators had been identified and probably executed in a raid, and the fabricated evidence had been broadcast by MSM, the invasion of Iraq would've been fairly easy to authorize via Congress.
Upon invasion of Iraq, some form of active WMD's would have been 'found', ie planted by US clandestine teams. Thus the invasion would've been justified on multiple levels, and the public would be none the wiser.
In reality, of course, none of this happened:
No Iraqis attacked America
No WMD's were used against America
No WMD's were 'found' in Iraq to justify the invasion
Every rational indication is that the US Gov was NOT involved in the 9/11 attacks, and that the collapse of the twin towers was not planned but was a coincidence - a success beyond the expectations of the real conspirators.
For 9/11 Truthers to continue to believe in the idea that the US plotted and carried out the attacks requires that the conspirators were at once:
Supremely powerful and astonishingly advanced in technology (never-before-seen weapons which leave no traces, and planted somehow without a single incidence of detection or suspicion)
Supremely incompetent, as they forgot they were trying to frame Iraq, and accidentally used Saudi conspirators, and with all their power, they also forgot to plant WMD's in Iraq!!
This is literally the story that truthers are trying to carry around in their heads, without realizing it, of course. Truthers appear to be the types of people who can carry around these kinds of gross contradictions without having them disturb their convictions. Most of us are forced to reject ideas that carry so many severe flaws and contradictions, unless we are considering them as fiction or fantasy. But that kind of suspension of disbelief is reserved for the enjoyment of Hollywood movies and other light entertainment - it should never be applied to real events, because it leads to true delusion.