It's Robert Perry who gives a careful perspective on distinguishing actual conspiracies from "conspiracy theories" in Contra-Cocaine Was a Real Conspiracy Consortium News 12/02/2013. He's referring to a political crime story, but it's a good perspective for skeptics looking at pseudoscience, quack medicine or UFO reports:
In my view, a "conspiracy theory" is a case of fanciful, usually fact-free speculation positing some alternative explanation for an event. Typically, a “conspiracy theory” not only lacks any real evidence but often ignores compelling evidence that goes in other directions. For instance, the current conspiracy theory about President Barack Obama being born in Kenya despite birth certificates and birth notices of his birth in Hawaii.Tags: conspiracy theories
By contrast, a real conspiracy can be defined as a collaboration among individuals to engage in criminal or scandalous behavior usually in a secretive manner. There are many such examples involving high government officials, including Richard Nixon’s Watergate and Ronald Reagan’s Iran-Contra Affair.
The difference between a “conspiracy theory” and a real conspiracy is that the latter is supported by substantial evidence and the former is reliant on someone simply thinking something up, often with partisan or ideological motivation.
There is, of course, much gray area between those two poles. There are cases in which some evidence exists indicating a conspiracy but it’s short of conclusive proof. In such cases of legitimate doubt, aggressive investigations are warranted – and the U.S. news media should welcome, not punish, these lines of inquiry.
Instead, the role of the mainstream press often has been to ridicule journalists and other investigators who venture into these murky waters. Often, that ridicule leads to serious cases of journalistic malfeasance as occurred with the mistreatment of Gary Webb and the Contra-cocaine story. ...
... each case is unique and should be treated as such. Each set of facts should be examined carefully.
Just because one conspiracy can be proven doesn’t substantiate every claim of conspiracy. And the opposite is also true, just because one fact-free conspiracy theory is nutty doesn’t mean all suspected conspiracies deserve ridicule. [my emphasis]