It would have been good to include a few entries here along the lines of "President Nixon tried to cover up the role of his re-election campaign in the Watergate break-in".

Hmm, this leads to an idea that maybe should go over in the experiment thread- see how good the general population is in saying they believe in actual conspiracies.

This does lead to a serious issue though, how do we distinguish the actual conspiracies from the non-conspiracies? See for example Cracked's Seven Insane Conspiracies That Actually Happened.

It seems that the set of actual conspiracies is much smaller than the set of claimed conspiracies so the prior is in general low. Also, most actual conspiracies are comparatively small scale and involve short-term interests compared to the general pool of conspiracies. However, there are some conspiracy theories that fall into this pattern that are generally considered to be in the crazy category- the most obvious two would be 9/11 conspiracy theories and JFK assassination theories. Thus, without actually looking at the evidence and motivation, it may be genuinely difficult to distinguish between the real and imagined conspiracies.