I suggest another 'test' that conspiracy theories should be held up to:

Assume that you are one of the ring-leaders, at the start of the planning phase of this conspiracy.

Assume that you wish to achieve their aims (according to the conspiracy theorists) - power, wealth, a war with the Middle East, accessing Iraqi oil supplies, whatever.

What courses of action are open to you? How risky is each? How costly?

Given the various alternatives, is it possible that you would select 'the conspiracy theory' as a suitable way forward?

I believe that the USA-involvement-in-9/11 conspiracy completely fails this test. There are so many simpler, cheaper, and safer ways for the USA administration to achieve the nefarious aims attributed to them by the conspiracy theorists - if they wanted to. Which one depends on what you believe the USA's aims were.

E.g. - Getting their hands in Iraqi oil. It would have been so much easier for the USA to cut a deal with Iraq than to engineer a war. The USA was the driving force behind maintaining the UN sanctions, and could have had them lifted if they wanted to. They could have negotiated almost anything with Sadam - exclusive oil deals, US military bases on Iraqi soil, etc. Sadam was a pragmatist above all else. With the USA with him, rather than against him...