Alex Knapp "defends" the birthers in a very detailed post. The conclusion:
While traditional adherence to quaint philosophic concepts might make it appear that the evidence overwhelmingly favors the conclusion that Barack Obama is a United States citizen, it is clear that this cannot be the case so long as we don’t pay any attention to the idea that there is an objective reality.
Cognitive Realism, the Law of Attraction, and Norse Mythology all provide plausible philosophic justification for ignoring evidence and logic. Accordingly, because Obama’s claim to American citizenship is only supported by evidence and logic, he must not be an American citizen. Thus, Barack Obama is not eligible to be President of the United States.
It’s perfectly logical.
If you're a Republican, a lot of things are logical: the entire debt began the moment Obama took office; Bush and Cheney never tortured anyone, but Obama is about to; the WMDs really are in Iraq; the president has the constitutional power to send tanks into the streets to arrest any American without charges; deficits don't matter; Obama is a Kenyan Muslim impostor; and Sarah Palin was qualified to be president of the United States at a moment's notice.
Politics as magical realism.