Here's an article I wrote for Blogcritics a few years back. It turns out that studies show that a person with a larger amygdala (a certain part of the brain) is significantly more likely to be conservative. Thing is, the larger the amygdala a person has, the more alert and oriented towards threats that person generally is. And IMO that's probably why the fear and conspiracy-theory claims are so prevalent in right-wing media and punditry - all of their ludicrous claims, accusations, and conspiracy theories are so silly to you and me...but to those who are more threat-oriented, such might well be very credible. This would explain why they simply don't see through all the silly crap they're being fed by right-wing media.
But what really sucks is that the research about the amygdala shows there might be a biological basis for all that. This biological basis doesn't make them better or worse, just more oriented towards threats.