Harmless conspiracies:

Shakespeare didn’t write his plays
Sherlock Holmes actually lived

That’s about it that I can think of. The rest fall under the category of….

Harmful conspiracies:

The Elders of Zion wrote a protocol
The CIA killed JFK and/or RFK
AGW is a hoax
Etc….
….and now this crap.

Wait, are we sure that Darwin’s theory of evolution is correct? Because I’m not feeling it right about now!