Here's how I approach all conspiracy theories – how many people would have to be involved and keep it a secret.
If 1 – 2 people then a conspiracy is probable if there is evidence of one
If 3 – 5 people then a conspiracy is possible
If 5 – 10 people then a conspiracy is highly unlikely
If over 10 people then no chance at all of a conspiracy working
If over 100 people, then you think the moon is made of cheese and the landings were faked
Now the conspiracy theory linked to is nuts. It is about the towers collapsing due to explosives presumably planted by the Government which were set off after the planes hit.
So how many people would have to be involved to hijack four planes, bypass WTC security, plant massive explosives, fake phone calls, fake radar records etc etc etc. I would suggest a cast of over 1,000 people were needed. Yep that's right over 1,000 Americans conspired to secretly murder 1000s of their fellow citizens, blow up the WTC etc and best of all not even a single one of them has ever leaked the truth.
It must be nice to be able to go visit other solar systems.