Conspiracy theories stem from the fact that people do not want to willingly accept the simple explanation. Two symbols of America brought down by a group of men armed with the simplest of tools, driven by religion and hate, fueled by terrifying determination... or....
A very complex plot involving oil companies, the president, drone aircraft, all the passengers being government employees (now in hiding), hidden explosives, saudi nationals, halliburton, and weapon releases from USAF interceptors.
I'd almost like to see one of these "experts" tell somebody who had a relative in the towers, on the first 2 planes, on flight 93... that their relative is part of the conspiracy and either wasn't on the plane, or didn't exist to begin with.