"They do overlap, but I can't tell you how big the overlap is," he said. "And, lizard people? Many people who are hearing voices would think that's crazy."
Duckworth argued that most mentally ill people create conspiracy theories that are self-centric, such as, "the mailman is after me," not inclusive such as, "the postal workers are all out to get us by 2015."
But others who treat schizophrenics and people with paranoia think there is a risk in circulating online conspiracies.
"Paranoid is wide category -- it's another way of being separate with reality -- but in our culture, we've made it synonymous with persecutory delusions," said MacDonald.
According to MacDonald, most delusions begin with general, unexplained feelings of discontent that are caused by a problem with the brain. It's only when someone tries to search for an explanation for their feelings that a delusion forms.
"Then over time, the delusions become crystallized -- meaning they take on particular narratives, story lines and people's motives begin to be fleshed out," said MacDonald. "When one thing isn't explained, it's never abandoned. The plot just thickens ... and you credit your persecutor with a tremendous amount of power."
MacDonald said it can make it difficult to do talk therapy when delusional people feed their story from outside sources or find evidence with other conspiracy plots.
"You're sitting across from your therapist and they say, 'Well why would they do all of this?' And you've got the answers because you've studied online," he said.
Icke said that sort of danger is not his responsibility.
"You can't stop information because it might be misused by people," he said.
"What people think of my information is none of my business; it's their business," he added. "I'm not saying, 'This is how it is, you must believe it.' I'm saying, 'This is another way to look at the world. What do you think?'"
Icke said he has run into psychiatrists analyzing why people believe his theories in television interviews.
To them, Icke says, "Check it out. Check it out. Then [decide]: Do the facts stand up? Don't go into this psychological babble after you first dismiss the information by reflex action."
Icke believes his popularity on the Internet is a testament to the validity of his ideas, and that people feel that his predictions have come to pass.
"What you do as you continue to research and you continue to travel is you hone it down," he said. "I've never come across anything that questioned the themes of what I'm talking about. ... With every day that passes, you just get more information."
"If the information over a period of time does not stand up to scrutiny and fact checking, it doesn't matter how far it will circulate, it's going to be dropped," he said.
After studying conspiracy theorists, Michael Barkun, professor of political science at Syracuse University and author of the book, "Culture of Conspiracy: Apocalyptic Visions in Contemporary America," said he thought image and packaging is actually key to attracting followers.
"Even someone whose ideas are deviant can produce a Web site that looks sleek and professional," said Barkun. "Those who have conspiracy theories to peddle can do it very easily. And if they're reasonably sophisticated, [they] can do it in a way that gives those ideas the appearance of validity."