part of the problem when it comes to science and discussions is what scientists mean by things, and what lay people (for want of a better word) mean are sometimes different things.
A for example.
Science can never, ever give you an absolte proof of anything. It can give you a very best estimate. For absolute proof you need maths.
I 'know', that if I drop a hammer it will fall to the ground. As a scientist I also know that there is an unbeleavably small possibility that all the atoms in the hammer will simultaneously shift at the same time, and the hammer may go back into my hand.
If you ask a scientist is this possible he will say 'yes, but very, very unlikly'. If a non scientis hear this you can imagige the banner headlines the next day. and this is what happens in some of the consipracy stuff. they ask a scientist 'Could this have happened, s/he may say 'Yes it could have' The next logical leap is that the teorist then says 'Scientist X confirms that this happened.' Which is not what s/he said.
Just because somethibg could have happened, it doesn't mean that it did happen. And untill you can be really sure in your theory, it is pointless to build a huge net of other theories on top of it. This isn't how science works.
So we go from, because it could withstand a hit from a 707 , it could have survived a hit hrom a 767, so it should have stayed uo and not fallen down, therefore it must have been blown up, therefore the CIA did it.
Because your first idea isn't proven (and in fact many experts will tell you that it couldn't wisthstand a 767 in that configuration), none of the rest are proven.