Sarah Palin is not an anomaly:
These guys have lived in an incestuous, consequence-free environment for so long that they no longer have the ability to self-edit. Something between 25 and 30% of the population lives so far removed from reality that they believe this stuff; given a random population distribution, some of them end up clumped together in large enough groups that people like Bachmann and Palin and a few others actually get elected to high office, and the Republican Party itself has become so bloated with conceit that it can't see the danger of trotting these people out before the rest of the country.
It's too bad the corrective cycle is so short nowadays. A hundred years ago a political party as fucked up as the Republicans wouldn't be able to untangle itself for a couple of decades, as happened to the Dems during the time of Bryan, for example. I suspect the Republicans will stop insulting the people's intelligence with empty-headed dumbasses like Palin and Bachmann real quick this time around.