In the images of the WTC Towers, there is clearly smoke and dust. I agree with you up to that point. However, there is no evidence that any of the dust is from steel, structural or otherwise. I have read one
analysis of dust samples collected after 9/11, and by far the majority components were gypsum (26% to 64% depending on sample) and concrete (14% to 31%). At most 1% of the dust was iron rich. Note: even iron rich dust did not necessarily come from the steel in the buildings.
I am sorry, but pictures of dust coming from collapsing buildings, a porous rock, and dust is not enough to convince me that this analysis is wrong. (Not to mention the fact that there are photos of massive piles of steel columns after the collapses, and all the other evidence that most of the steel survived.)