Its become obvious that the reason behind the entire ‘truther’ movement is that 9/11 completely screwed the hard-left pacifists worldview:
1. there are no enemies to the hard-left’s left
2. there is no reason to ever go to war
3. there are no external enemies of America, only internal conservative enemies
4. white people are always the oppressors, never the victims
5. George W. Bush (and the Republicans) must never get credit for doing anything right, for doing anything for just motives, or for succeeding in any way, shape or form
9/11 so wrecked this world-view that the hard-left’s entire universe was rocked. The only solution was obvious: it didn’t happen. There are no Islamofascits. Osama and Al-Qaeda are not and never have been a threat to the US. Saddam had nothing to do with Al-Qaeda in any case, and he himself was never a threat to the US.
9/11 was an inside job by the internal enemies of the US, with Al Qaeda used as a scapegoat. Osama was happy to take credit to shore up his bona fides among the faithful. GWB used 9/11 to consolidate power and use it in the Middle East to avenge his Dad/grab oil/what have you.
Trutherism is an example of the Big Lie. Tell it loudly and often enough and people will start to believe it, against all rational evidence to the contrary.