You make it seem as if this association between "rational" and "irrational" conspiracy theorists is itself a conspiracy to discredit the former with the latter, which probably happens, but it's also the case that the conspiracy theorist community (or communities) and conspiracy sites often choose not to discriminate between rational and irrational theory themselves. Conspiracists tend to interpret skepticism or attempts to debunk (read, actually prove) their theories as attempts to "silence the truth," making it difficult to clean house.

Although it also doesn't help that the more outlandish conspiracy theories are the ones that enter public consciousness through the media. But those outlandish conspiracy theories are also the most fun - would anyone watch an X Files about normal, boring conspiracies - tax evasion, surveillance and occasional human experimentation, rather than aliens and the Illuminati?

>Such examples, along with others in my years on the conspiracy beat, are emblematic of a trend I have detected that people who believe in one such theory tend to believe in many other equally improbable and often contradictory cabals. This observation has recently been confirmed empirically by University of Kent psychologists Michael J. Wood, Karen M. Douglas and Robbie M. Sutton in a paper entitled “Dead and Alive: Beliefs in Contradictory Conspiracy Theories,” published in the journal Social Psychological and Personality Science this past January. The authors begin by defining a conspiracy theory as “a proposed plot by powerful people or organizations working together in secret to accomplish some (usually sinister) goal” that is “notoriously resistant to falsification … with new layers of conspiracy being added to rationalize each new piece of disconfirming evidence.” Once you believe that “one massive, sinister conspiracy could be successfully executed in near-perfect secrecy, [it] suggests that many such plots are possible.” With this cabalistic paradigm in place, conspiracies can become “the default explanation for any given event—a unitary, closed-off worldview in which beliefs come together in a mutually supportive network known as a monological belief system.”

>This monological belief system explains the significant correlations between different conspiracy theories in the study. For example, “a belief that a rogue cell of MI6 was responsible for [Princess] Diana's death was correlated with belief in theories that HIV was created in a laboratory … that the moon landing was a hoax … and that governments are covering up the existence of aliens.” The effect continues even when the conspiracies contradict one another: the more participants believed that Diana faked her own death, the more they believed that she was murdered.

Fun to hang out with, though.