The great thing about conspiracy theories is that they only have to make sense within their own context, which they conveniently create. Once you're inside the bubble, every fact becomes new evidence of the theory and every fact that disproves the conspiracy theory becomes evidence of a coverup, which ends up lending credence to the conspiracy theory all over again. This is how people find themselves believing that the Smithsonian Institute is actively engaged in a massive coverup to hide proof that giant half-alien hybrids colonized the US in the 5th century, among other less intellectually defensible positions. Never mind that it makes absolutely no sense, once you're convinced that those giant alien-human hybrids existed and learn there's no evidence, then logic (such as it is) immediately dictates that the evidence must have been destroyed. The alternative - that there never were any half-alien power forwards lurching across the landscape during the Moundbuilder period and the whole concept is loonier than a pile of Canadian currency - is unthinkable.
