I have been through the entire set of arguments about the 911 cover up so many times with people that it has become easy to predict the common positions that people will take in defense of their world view. I say in defense of their world view, because that's exactly what it is. Accepting the truth about the events of 911 would be absolutely devastating to their reality.
One of my favorite arguments is the one that comes up when I talk to people about the velocity of objects falling through space in a vacuum and the speed that the WTC towers fell.
An object falling through space with absolutely 0 resistance, not even the resistance of air would have taken 9.22 seconds to hit the ground, yet by official record one of the buildings fell in approximately 8 seconds.
This isn't possible without some force pushing the building down from above; more specifically explosives.