The argument in its unsimplified mantra is that in order to "prove" something, it should be reproducible. Since there no precedent of a large building collapsing, (or rather more appropriately due to fire initiating it), and rebuilding exact replicas of the WTC is out of the question, "truthers" believe the existing conclusion that fire was responsible in the WTC events are "not proven."
Rather than going the competent route and examining code compliance, construction methods and materials, event circumstances, material specs, modeling, study of partial collapse events and figuring out why results were dissimilar and the like, you would rather say that it's "unproven" on the grounds of a lack of physical evidence, or say, that "many buildings are known to collapse when explosives are planted in them" as some members put it.
In fact you have rejected several venues that are used in professional practice which are applied before a building is ever erected, material tables and calculations not only based on real samples, but proven methods. You will of course, predictably
nitpick my posts without reading it properly, as I've had to deal with twice already in this very thread.
[EDIT: What I understood this thread to be about was for those claiming it's not proven, to offer some if not all of those areas - examining code compliance, construction methods and materials, event circumstances, material specs, modeling, study of partial collapse events and figuring out why results were dissimilar and the like - to justify such claims as "the collapse theory remains unproven." Nobody seems to want to give it shot. On this this forum it's somewhat understandable given the head wind that some "truthers" have to deal with just by supporting CD, etc theories, but groups like AE911truth whom avoid these issues like the plague, whos activities are not influenced by JREF have no excuses.