Reference Alert
Popular Mechanics is famous for "debunking" 9-11 "conspiracy theories" in the laziest way possible; they erect straw man arguments and then ride to the rescue to knock them down. "Some 9-11 conspiracy wingnuts even claim that space aliens did it. That's just silly talk. So logically, the government's story _has_ to be true." These "hit pieces" are easy to do in the pages of one's own magazine, but they don't stand up to an informed 9-11 Truther. The guy _had_ to cancel; he was going to get his ass handed to him.
Take even the most tongue-tied, ineloquent, disorganized 9-11 Truther and he will still win a debate.* All he has to do is pluck nuggets of truth from the 9-11 Truth Tree. He's got binders full of facts. His most difficult task is picking one.
It's no surprise that Popular Mechanics pulled out of the debate; it was a no-win.
No one ever wants to debate a 9-11 Truther on the facts:
...How did Building Seven fall right down? ...I'm all ears...
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*Postscript: I don't know what 9-11 Truther was slated to debate him. This piece doesn't involve him. It's not supposed to speak that way.