The best way to understand a good many things is to look at overall patterns of evidence. Reductionists (like most debunkers, as opposed to truly open minded skeptics) like to ignore those disturbing patterns and focus on a few of the weakest pieces of evidence they can find. There is a pattern of evidence surrounding Dallas, a pattern for Oklahoma City, one for the death of Vince Foster, and so on. So let's summarize some of the best evidence for a 9/11 conspiracy, and look at the pattern.
First of all, before 9/11, no steel framed building had ever completely collapsed due to fire, and only one had partly collapsed, after many hours. But on 9/11, three of them allegedly collapsed due to a rather smoky fire. Video taken by the news media, not by conspiracy buffs, slowed down, clearly shows a large tank protruding below the belly of one of the "airliners," showing that, in fact, it was not an airliner. The towers and Building Seven all collapsed straight down, a feat virtually impossible to achieve without the use of carefully pre-planned controlled demolitions. Videos clearly show that the buildings collapsed at free fall speed, which is not possible if floors pancaked one on the next, as there would be a slight delay with each impact. News media videotapes show explosions at multiple levels, and firefighters heard multiple explosions preceding the collapse. A seismic center of the USGS picked up the shock wave from an explosion in one of the basements.
Building Seven was scarcely damaged at all by fire and never struck by an "airliner," and firefighters insisted that they had its fires under control, when the lease holder ordered them out and announced that they would "pull" the building, which means set off controlled demolition charges.
Two airliners had already struck buildings when the flight that allegedly hit the Pentagon (you know, the invisible plane that cannot be seen in the few videos made public) went off course, ignored ground control, and headed straight for DC, which, even before 9/11, was a max security area protected by fighter planes and missiles. Yet no one intercepted it, or any of the "airliners" that day. This in itself is mind boggling. The hole in the Pentagon was too small for an airliner, and little things like bodies of the passengers, wings, etc., were never found. The tiny bit of wreckage from the plane that allegedly crashed in Pennsylvania is scattered over a large area, explainable only by an explosion at high altitude.
Add to this the fact that FBI field agents and the Pentagon's Able Danger team tried repeatedly to warn their superiors about Arabs with terrorist links seeking flight training. And the fact that the passport of one of the alleged terrorists magically flew out of his pocket, through the wall of the plane, backward as the plane moved forward at several hundred miles per hour, passed through all the fire, landed in the street amid piles of debris and was miraculously found by our intrepid FBI men, who also, in hours, had the names of all the terrorists they had been unable to stop. But the plane' flight recorder, designed to withstand impact, crushing, and fire, was never found.
There's more, but that's why entire books have been written on this subject. William B Stoecker