I used to be a conspiracy nut at one point in my life. I believed in the worldwide, big brother, government-wide conspiracies that became the stuff of legend. After a while of thinking about it, common sense took over and things began to make sense. I started looking at the supposed scope of these conspiracies and realized that most of them were improbable or unlikely. It's not too difficult to disqualify a conspiracy based on any number of factors.
The number of people it would take to carry out a supposed plot is one of the biggest giveaways. Conspiracies that require a lot of people are not as likely because it is more likely that somebody would come forward and say something. Classic big brother plots, where some agency is watching everyone all of the time are highly unlikely because of the sheer number of people required. Even if one person watched one thousand people all day and night, this plot would require 300,000 people just to keep watch. The moon landing required a lot of people which makes it unlikely, but it was also repeated five more times.
Normally, if the conspiracy is not on-going, then it's done once and that's all. Trying something more than once runs the risk of going wrong and getting uncovered. The moon landing falls to this factor because it was done six total times and nobody could explain why on the hoax believer side of things. Just for the record, I have never doubted the moon landings at all. Science conspiracies are an example of repeated conspiracies, but they also fall under a special category that I will call formulaic conspiracies.
The recent "Climategate" conspiracy has got me thinking about other conspiracies of science. The biggest problem with trying to debunk science is the unfailing system of checks and balances that are built in. The "Climategate" issue has people calling climate change a big hoax, but the truth is, the data that climatologists are using is also being used in other sciences that may be unrelated to climate change. The data and formulas are peer reviewed prior to being pubblished along with being used in other areas. If that data was fake then it would mean that either the other sciences have fake results or they will find the bad data and take back for further review. It's hard to prove science conspiracies because of this level of overview.
There is also the matter that these plots are allegedly carried out by the smartest and most-secretive entities in the government, but it seems that the most unsophisticated doofuses (doofi?) seem to know everything about the plot. If the best, brightest and most secretive are pulling this off then how could half of the morons who claim to know what is going on really know? It does not stand to reason and, therefore, it is less likely that anything is really happening. In most cases, conspiracy theories come from people's overly active imagination or from movies and books. The surest sign that there is no conspiracy is that you're convinced that there is one.