Until concrete evidence is provided, we cannot make such an assumption. The default stance of this conspiracy theory is “Prove it WASN’T an inside job!”, which is much like Bush saying to Iraq “Prove you DON’T have weapons of mass destruction.” That’s a stance that proves no solid evidence, merely conjecture and speculation which hardly qualify as proof. The 3rd structure in the WTC was on fire for HOURS because they basically pulled out and called it a lost cause. Building that are let to burn for hours tend to fall. As for the pentagon, there was luggage found so unless Pentagon employees tend to bring fully packed luggage with them to work every day, it stands to reasons that an airplane might have crashed into it. Also, a plane flying at full speed into the Pentagon, a highly fortified structure, would cause a certain amount of disintegration (plane breaking apart) so while there wasn’t anything like a jet engine seen on the aftermath photos, there were other smaller parts found in the debris. There were also a lot of phone calls made from the plane’s phones. One last thing… if a plane didnt hit the pentagon, where’s the plane? Where’s the people on board? These things dont disappear into the ether.