Dear sinkspur,
"One can never beat a conspiracist in an argument, because there's always another boogey man around the corner."
Actually, the technical term for this is the non-falsifiability of a hypothesis.
Evidence for the conspiracy is taken as just that: evidence for the conspiracy. Evidence that tells against the conspiracy is re-interpreted as evidence that the conspiracy is all the more effective; the conspiracy is even able to produce "counter-factual evidence" ostensibly disproving the conspiracy.
When you've reached that point regarding any topic, it's time to resort to psychotropic drugs.
sitetest
Usually at that point, I resort to a quart or two of Black Jack. Cheaper, and better results.