Poll any segment of society and you'll find that a not-insignificant portion of people believe in a wide range of conspiracy theories, but apparently the idea that President Obama is a secret-Kenyan usurper is especially popular among Republicans.
[A] new study from Fairleigh Dickinson University suggests that so-called birthers are far more numerous than previously thought. Sixty four percent of Republicans polled by the university’s PublicMind project said that it was “probably true” that Obama is hiding details of his personal history, including possibly his birth place. Also polled were the conspiracy theories that the 9/11 attacks were an inside job (25 percent of all respondents said that was “probably true”), that President Bush stole the 2004 election (23 percent), and that Obama stole the 2012 election (20 percent).
The most widely-believed theory among Democrats is the idea that Bush stole the 2004 election at 37 percent.
I may be biased, but I think that theory is relatively harmless compared to the racially-tinged theory that President Obama wasn't actually born in this country. And the percentage of Democrats who believe in any given theory is apparently much lower.
As for why Republicans are more likely to believe in conspiracy theories than Democrats, the study did provide a possible explanation.
“There are several possible explanations for this,” said Fairleigh Dickinson political scientist Dan Cassino, who helped conduct the poll. “It could be that more conspiracy-minded Republicans seek out more information, or that the information some Republicans seek out just tends to reinforce these myths.”
Republicans are more likely to believe in conspiracies because Fox News, Glenn Beck, Boss Limbaugh, and the rest of Hate Radio are making a lot of money by feeding it to them. It's the conservative entertainment complex.