Why some people dare question the reality of 9/11, with this absurd conspiracy theory? Are those people insane?

Although I don't believe the theory, I think it's a great fact that people question this. If everybody would blindly follow what the government tells them, no one would think for themselves and everybody would basically be brainwashed. And the theory was pretty good and convincing if you really look into it, but still I don't believe they would do something like this.