Well, the Crackpot Index is obviously tongue in cheek, but also born out of frustration, I think. It must get tiresome for scientists to listen to cranks trying

Well, the Crackpot Index is obviously tongue in cheek, but also born out of frustration, I think. It must get tiresome for scientists to listen to cranks trying to "disprove" established science with bizarre theories and a complete disregard for the literature. You can address one, two, three of these people, but it soon becomes a bother and you're tempted to write the Index instead. I agree it's probably very difficult to tell really novel and paradigm-shifting theories from the ramblings of cranks. I suppose the Dark Matter model scores highly in some items of the Crackpot Index but very low in "the government is trying to suppress this", "everything they told you is a lie", and also the scientists who proposed it understood the established science and didn't randomly disregard it. I think the "conspiracy" aspect is what sets a crackpot apart. Again, it's possible that a person is a crackpot AND he/she is also right about a particular theory!