Legit you people have an understanding of physics on par with a kindergartener or maybe even a preschooler.

1. A skyscraper depends entirely on a network of precisely designed and placed beams and supports to channel and distribute the load of each additional floor. While obviously there is redundancy in the way these structures are designed, damage to these load bearing components, especially asymmetric damage or damage to multiple adjacent floors, greatly compromises the structure's ability to support its own weight. Combine this with a fire and its only a matter of time before catastrophic failure.

2. Lets ignore the specifics of the WTC for a moment and just imagine that parts of an upper floor break loose in a tall building. By the time those parts hit the floor below, they'll be imparting a much greater force on the structure than they were when they were stationary. If that force is enough to break the floor below, you'll now have 2 floors worth of debris coming down on the next floor below which will now definitely fail under the increased weight. Repeat this process x50 and it ends up being a whole lot like what happened on 9/11.

3. Are you expecting that a skyscraper would fall over like a tree rather than collapse? Think for a minute about what such a motion would require. At a bare minimum, the structure at the pivot point would need to be able to support the entire weight of all the upper floors rather than the 1/4-1/2 that it was previously holding, even as the tilt would start pushing the pivot point outward. Then you'd also need the upper floors themselves to remain completely rigid as they begin rotating around the pivot, even though they were not in any way designed to handle those kinds of loads.