Lets look at some of the possibilities shall we:
- Hoaxes either for fun or to drive market stocks/shares up or down
- Heard from a friend of a friend
- Disinformation by a company and/or government
- Adverts for the next blockbuster
- Science thought to be controlled by dark forces...
- Every secret society ever (obviously not that secret)
- Anyone famous, were they killed?
- Lets us not forget Godwin's Rule
- Fiction seen as Fact
- Genuine article
And the problem with that genuine article is that it is still a theory based upon hopefully common sense reasoning and maybe some facts that normally fail to prove anything definite otherwise it wouldn't a be theory.
For any theory it should about making the theory fit the facts and not the other way. Scientists discovering that the universe was missing some matter because it didn't fit into observable results invented Dark Matter so everything fitted together again. This is a well accepted theory, it however smacks of changing the facts to fit the theory. Why do I bring this up, because human nature is the same the world over we love stories and inventing facts to fit our theories, but then I'm generalising like I always do.