To make matters worse, socially-defined beliefs add tremendous bias. Whereas most people stop believing in Santa, the Tooth Fairy, etc., because of implausability or lack of evidence, peer expectations can override that doubt. Religious doctrine is an example. No one believes it physically possible that Noah could have made an ark that big, or crammed two of every species on the boat, but that doesn't prevent many people from believing that the story is true. Ironically, people use knowledge of this susceptibility to irrational belief to support their own irrational belief systems (i.e. "Anthropogenic global warming is a mass delusion"), because their own belief is that an opposing group is irrational. Even more ironically, they are correct because the other group has an irrational majority. Most people do not believe that anthropogenic global warming is real because of the evidence, but because their peers have convinced them so. Just because someone is correct, it doesn't mean that they arrived at their conclusion rationally. Also, just because someone has a socially-defined belief, it doesn't mean they are incorrect.
You seem intent on the "rationality" of conspiracy theories and belief, probably because 538 doesn't give a shit about behavioral psychology. This doesn't serve them well, and it won't serve you well either. Our belief in "Santa, the Tooth Fairy, etc" are not rationally-derived or rationally defended, they are dogma we outgrow. No kid goes "presents appear therefore Santa" they go "my parents told me this thing and I have no reason to question their assertions." Psychologically speaking, religion holds few examples that can be extrapolated to conspiratorial thinking. Religious doctrine is not a conspiracy theory, it's a shared cultural heritage. The idea of "Noah's Ark" occupies a different place than the idea of "911 was an inside job" in our thoughts and in our behavior. "Noah's Ark" is a belief system that we use for affinity with others; "911 was an inside job" is a belief system that we use to distinguish ourselves from others. "Noah's Ark" is a cultural touchstone we inherit from cultural leaders while "911 was an inside job" is a cultural erosion we seek out from the margins. If you want to throw Santa into the mix, a disbelief in Santa is the conspiracy theory: by investigating whether or not Santa exists, children are defying their cultural heritage. Conspiratorial thinking is now and has always been a minority sentiment. Alternative theories from within the power structure are seen as advancement while alternative theories from without the power structure are seen as conspiratorial. When the power structure is strong the conspiracies tend to die out, or at least fail to overthrow the prevailing conventional wisdom. Kabbalah emerged about the same time as Protestantism but the Jewish social and religious structure was strong, so Kabbalah remained fringe. On the other hand, the Catholic power structure had been weakened by centuries of venality so Martin Luther reshaped Europe. This sort of thinking gives short shrift to both groups. Neither group thinks the other is irrational, they discount the veracity and authenticity of each others' information. Anthropocentric global warming is a perfect example - both sides are picking data from a public historical record and coming to different conclusions through the selection of supportive information. And this is just condescending. Society is not a group of peers, society is a hierarchy. Those who accept anthropocentric global warming accept the conclusions of experts whose expertise they accept. Those "experts" might very well include Kim Kardashian but sociologically, they are "experts" nonetheless. Humans do not occupy a flat hierarchy. Our acceptance or rejection of conventional wisdom is not at all related to our peers, it is a function of our conception of the hierarchy we occupy, our place in it, and the place of those we interact with. The arrival of social media and the visible flattening of media production forces a restructuring of our "trust" hierarchy and for some people, Jim Watkins ends up in a better place than Lester Holt. That doesn't make people irrational. That doesn't make conspiracy theories logical fallacies. It means that society functions on trust and our trust in social structures has been on the decline since the assassination of JFK.Ironically, people use knowledge of this susceptibility to irrational belief to support their own irrational belief systems (i.e. "Anthropogenic global warming is a mass delusion"), because their own belief is that an opposing group is irrational.
Most people do not believe that anthropogenic global warming is real because of the evidence, but because their peers have convinced them so.