In my opinion, just because a conspiricacy theorist talks rubbish it doesn't mean he/she is insane.

Of course there is one way to disprove the 9/11 conspiracy theorists -to deliberately fly a passenger jet, fully fuelled with accelerant into the side of a tall building under strictly controlled conditions.

So any qualified pilots prepared to give it a go? and do any airlines have a spare airliner they won't miss, and does any city have a skyscaper they are a bit fed up of?

The point about this is that it is much easier for a conspiracy theorist to argue the plausibility of his or her idea, whereas the real world has to make do with empirical evidence.