First of all, let me say that I found the video "Loose Change" uncompelling and a poor presentation of the facts surrounding 9/11. So I will not speak with regard to the film. However, I would like to comment with regard to the facts themselves.
The point you you make in challenging the theory that WTC Building 7 was deliberately brought down is that you know someone at Controlled Demolitions Inc. who told you that WTC Building 7 was not taken down in a controlled demolition, and that you trust in his judgment. I would simply observe that this is an appeal to authority, and not an argument. This person's judgment is not an explanation of the facts.
Beyond this appeal to authority, you merely noted that the building had been damaged by falling debris from the WTC towers 1 and 2 and that there were fires in the building. Apparently, you believe that the structural damage along with the fires would be sufficient enough to explain the perfectly symetrical collapse. I disagree with you that this is sufficient. To date, no investigation into the collapse of the building has sufficiently explained what happened (and the 9/11 Commission report doesn't even relegate it to so much as a footnote).
It's all well to appeal to authority, but explanations are required, and opinions insufficient. I suggest you watch the videos of WTC 7 collapsing and have your source explain to you how it is physically possible for the limited structural damage and fires to cause the complete and simultaneous failure of all major support columns in a 47 story steel framed skyscraper. I would love to know how your expert source explains this seemingly physically impossible phenomenon.
Since you have made yourself so familiar with controlled demolitions by watching various documentaires, you must know that it is only by cutting all major load-bearing columns simultaneously that a building is able to fall into its own footprint. In fact, demolitions experts often want a building to collapse in one direction and cause it to topple over onto its side by cutting columns sequentially rather than simultaneously (that is to say, by blowing columns on one side first followed by the other side after a delay, rather than at the same time).
There are other basic things to consider, as well. The failure of load-bearing columns in one part of a building would not necessarily result in a "chain reaction" type failure of all columns. So even if one side of a building collapsed completely, another side might remain standing. This is true of reinforced concrete as well as steel-framed structures. You mentioned Oklahoma City. With regard to that, I would observe that even though one complete side of the building was blown away and collapsed completely, the building still stood. WTC buildings 4, 5, and 6 are further examples. One of the websites you referred to has a photo of the Banker's Trust building, which suffered severe damage from WTC debris (far more extensive than WTC 7). It didn't collapse (naturally; we shouldn't have expected it to).
Even if there were some sort of chain reaction resulting in a total collapse (which would have to be explained physically based on the building's design and forensic evidence), it would not be a total simultaneous failure, but a progressive one. If such was the nature of the WTC 7 collapse, if it was truly such an accidental progressive failure of the load-bearing support structure, how can your source explain the fact that the building "imploded" so perfectly. This defies common sense and requires further explanation.
It seems fairly self evident to me that it is physically impossible for every load-bearing column in WTC 7 to have failed at precisely the same time if the cause was structural and fire damage. I hope you contact your source again and inquire as to their explanation for this apparent inconsistency. I would love to learn from you what his or her answer to this mystery is.
Read Mary's article: 9/11: Challenging 'Loose Change'