I would like to start by defining the rules of conspiracy theories. They differ from normal thought and logic, but they tend to follow these general rules.
1. It is only necessary to observe the evidence that you wish to.
For example, the moonbats who believe that a cruise missile hit the Pentagon. As "proof" of this they cite a man who said he saw a plane hit the pentagon "like a cruise missile", ignoring the concept of a simile, and the fact that he, along with thousands of other people saw a "plane" hit the pentagon.
2. A lack of evidence is only proof of the depth of the cover-up.
Pretty self explanatory, I would have the evidence if only they hadn't covered it up so well!
3. Anyone who doesn't agree with a conspiracy theory is either part of the cover-up (see rule 2) or just a close minded drone of the government.
4. The law of inverse proportionality of authority.
The validity of any source is inversely proportional to its authoritativeness .
Any government commission, serious academic (not those who teach humanities at Berkeley), law enforcement official, or politician, ie. the people who are in the position to actually know, are immediately suspect because they were probably involved in the conspiracy in the first place. Someone completely removed from the situation, like some guy posting on his website while watching reruns of Star Trek in his parents' basement is more likely to be untainted.
5. Occams corollary: The complexity and difficulty of a conspiracy theory is only proof of the depth and deviousness of the conspiracy.
6. The Law of Infinite Permutations: Even in the case that an infinite amount of statements are proven wrong an equally infinite amount of new statements can be made.
For example: in the discussion I had the moonbat asserted that no black boxes were found from the 9/11 crashes. When I pointed out that the black boxes from the Pentagon and Pennsylvania crashes had in fact been found, he changed his argument to "OK, well 2 of them have been found, but the data has not been released". I then pointed out that in fact they played the cockpit voice recorders to members of the families who requested. His argument then changed to, well they were probably faked. And this of course can go on ad infinitum.
In mathematical terms:
Conspiracy Theorist (CT) states 2 + 2 = 5
Level Headed Skeptic (LHS) proves this is false 2 + 2 = 4
CT counters, no 2 + 3 = 6
LHS proves otherwise, 2 + 3 = 5
CT counters, no 2 + 4 = 7...
And this of course goes on forever. Thus CT can never actually be proven wrong.