Such an elaborate conspiracy would be pretty much impossible.

But still- why did all three towers collapse? Can a building fire, even one augmented by jet fuel (assuming that didn't all burn off quickly) heat steel enough to weaken it to failure? Especially when the structure acts as a gigantic heat sink? And WTC7 didn't have the jet fuel.

From the NIST report:

Majority of steel found stronger than minimum requirements. Approximately 87 percent of the recovered WTC steel specimens tested exceeded the required minimum yield strengths specified in the building design criteria; some 13 percent did not. However, the safety of the towers was most likely not affected by the small percentage of steel below the minimum. Building designs routinely allow structures to withstand greater loads than are expected by including significant factors of safety. Moreover, the structural loads on Sept. 11, 2001, were well below this design level.

NIST

If the "doughnuts on a broomstick" analogy is correct, then would it not only require one or two floors to collapse? Making a "conspiracy" a lot more do-able. Not saying it happened, just that it might not be impossible on this scale. Planning for the jet impacts would be tough, though.