"People's pre-existing personality biases, they find, actually shape their beliefs about the factual reality of the world; more information is unlikely to produce consensus, because people tend to reject information that does not cohere with their worldview."
The Economist blogger's further reasoning:
"A substantial number of Americans came to insist that torturing suspected terrorists was acceptable because it was a practice identified with the people they had voted for, and because it was behaviour that American troops had engaged in. The same process occurred with belief in the existence of WMD in Iraq, and, in some countries, with the 9/11 "truther" scenarios, which retain an irrational hold in many quarters; and it also seems to have occurred with climate change. We have a dynamic of political discourse that produces absolute belief in things that, often enough, aren't true. I don't believe there is any further data that could cause people who still deny the reality of anthropogenic global warming to change their minds."
Basically, people believe in irrational theories because the people who they want to lead them become associated with irrational theories. And, at this point, there is precious little that can be said that would actually convince these people otherwise, as they hold that they are "bucking the trend" or "fighting the consensus". In other words, they are being different because they want to be different and think that they are being individuals, instead of being "sheeple". It reminds me of something Ricky Gervais once said about why conspiracy theorists are obnoxious, because they think that they are just too smart because they've figured out what's "really" going on. Instead of proving how much smarter they are, they usually end up doing the opposite...