In general, I think those who believe in conspiracy theories have small minds. They need to have an event packaged so they can believe it--it's too difficult to accept that radical Muslims could hijack aircraft and fly them into buildings. No, that's not enough, there has to be more.
No amount of fact or reason will convince them of reality, because reality is too difficult for them. Better just to believe that Uncle Sugar--who can't fight a war correctly, who wastes billions, whose incompetence is matched only by his bloat (all of this in their eyes)--could pull off something like September 11th. Better to believe that George Bush, simpleton dimwit that he is, could pull off this masterful operation and blame it on radical Muslims. Good that the conspiracy theorists are smarter than the rest of us, so they can see through Chimpy McBushitler's evil ways and alert the rest of us. Like Cassandra, though, they tell the truth but we are fated not to believe them.
Small minds, with just a touch of egomania.
Don't try to argue with or convince the simpletons. May as well try to teach my dog to play a Bach concerto. But conspiracy theories often have a grain of "what if..." or "what about..." in them, waiting to snag even a thinking person. Worried about that, about getting caught up in a maelstrom that turns out, upon logical examination, to be a tempest in a teapot? Then read this.