Here is my theory:
The WTC needed to be destroyed and desguised as a terror attack so Bush could go to war with Afghanistan.
In order fool the public into thinking it was caused by Arab terrorists, actual Arab terrorists were employed to hi-jack airliners and fly them into the WTC.
Airliners had to be hi-jacked in order to make people believe Arab terrorists flew them into the WTC and caused the buildings to collapse, because no one would ever beleive that Arab terrorists would be smart enough to bomb the WTC and try to bring it down, despite having tried exactly this before.
Hey kappa, wouldn't it have been a lot easier to just plant the bombs and blow up the buildings rather than bring the planes into the building, then detonating the bombs? What was the reason for even using the planes?
If the bombs could be planted and nobody detected them, why not just set them off and blame terrorists?
Can I borrow your foil hat sometime?