LGear
Secret Society BLANKET
But does it? For the most part, it seems to be banking on the assumption that such a person is not credible, which is why it's such a shocking affair to find out that they are. Like the large brute that turns out to be intelligent or the beautiful woman that can fight, it depends on our assumptions of what a character should be like.
That's exactly why I don't like it: it's a specific instance of a trope subversion used enough times that it has become the trope, that when an audience sees someone trying to peddle a conspiracy theory in a plot, they're now more than likely to believe them because they're "the conspiracy theorist", and unfortunately in turn said assumption has spilled out into mainstream thinking.