Seth Godin argues:

A conspiracy theory is a complex, alternative explanation for the truth. By definition, they’re not true. Of course there are plenty of things that are the result of conspiracies. Call them conspiracy facts instead of theories. Countries, organizations and movies are often the result of people conspiring together, sometimes in secret..

“A conspiracy theory is a complex, alternative explanation for the truth. By definition, they’re not true.” .. umm by that definition they are not true. Conspiracy theories question the validity of an official story that purports to explains something and present alternate explanatory stories. A conspiracy theory is valid and worthy of our consideration to the extent that it presents facts that contradict the official story.

The former prime minister of Malaysia Dr Mahathir Mohamad is apparently a 9/11 conspiracy theorist.