Erasmo points out, in effect, that I am using a priori reasoning to justify ignoring empirical evidence. This is itself a very unscientific thing to do. So I am the one who is being unscientific and not (necessarily) the conspiracy "theorist."
He is quite right that by implication I am saying that scientists and scholars are right to ignore the latest conspiracy theory, without even looking at the evidence for that theory. But I would add that a priori reasoning, of this sort, is not alien to science at all.
Suppose I am an astronomer, specializing in the study of planets. I am deluged with new findings about extrasolar planets, more than I can keep up with. One fine day I get a self-published monograph in the mail, detailing "new evidence" that planet earth is flat. You know what I am going to do. I'm going to toss the book, and without looking at the new evidence. Is this unscientific? Is this irrational?