1. Be kinda hard to hide the amount of explosives that would be needed to bring down WTC 7, much moreso to actually smuggle them into the WTC 7 and properly set them up unnoticed to create such a demolition.
2. As for people trying to debunk Bin Laden's claims it is ridiculous. People that claim this are hedging their bets that the people are so ignorant that they won't go watch his tapes for themselves. I suppose it is effective seeing as according to youtube only a few thousand of us in the entire world have ever investigated Bin Laden at length. You can watch all his interviews and all his tapes right on youtube. Ain't no secret, therefore it is no conspiracy. Listen for yourself. Osama tells you pretty bluntly he did 9/11 and goes down to the details even. I recommend starting with the interview I posted on page 1, but there's many other videos or audios of Bin Laden that can be used to corroborate his involvement.
3. There's always loose ends, there is a way to figure out any conspiracy, theory, or conspiracy theory. To pull off an attack of the magnitude of 9/11 is gonna leave many trails to trace. All the roads lead back to an Islam-inspired attack masterminded or supported by Bin Laden or Saudi Arabia.