I don't know. I tend to think most of the people who claim to know sound nuts. But I'm more inclined to believe there ~might~ be a conspiracy to cover up something that's known on the second than the first.
You have a point. I read most of an online book about OKC that tried to argue McVeigh had some kind of mind control implant. Could be, but the author should have used the tinfoil tag or something... The difficulty in weighing the evidence the conspiracy fringe brings to light is the fact that there are two sorts who are drawn to conspiracy theories. The first group is rational, and simply see evidence that logically leads them to question the official line. If they are wrong, they are OK with it because they don't get personally invested in it.
For example, if all the things that I think point to Joel III being a terrorist plot gone sour turn out to be adequately explained within the lone, depressed kid killing himself theory, I don't care. I'm happy to be wrong because my paradigm is still that we live in the greatest, richest, most free country in the history of the planet, and man (in this country) is generally good and our institutions are generally honorable. But when the second kind of conspiracy theorest gets proven wrong, there is always a backup, even more kookier explanation, even more improbable than the first. This theorest has to keep going down that path because he is personally invested in the outcome. If he is wrong, his entire world view comes into question. That is the one thing most folks are totally unwilling to challenge.
I think we can agree, then, that healthy skepticism is always in order, that asking questions is good, and that the opinions formed should be based on the best, simplest understanding of the evidence.