Asbestos was probably a contributing factor on the tower collapses but not in the way you think. Asbestos was banned when the WTC towers were under construction so it was not used on anything above the 64th floor. The lack of asbestos on the support structures made them more susceptible to damage from high heat and the lack also made fire spread more rapidly. The modifications that had to be made to mid-way through construction to provide fire resistance to the upper floors made them heavier then the lower floors where asbestos was used. None of what I just wrote is meant to discredit 9-11 being an inside job - just pointing out known weaknesses in the WTC construction as it relates to asbestos and weight.