This excerpt below tends to explain why so many right-wingers still cling to the "birther" conspiracy theory despite it being debunked time after time:

The problem not only with fundamentalist Christians but with Republicans in general is not that they act on blind faith, without thinking. The problem is that they are incorrigible doubters with an insatiable appetite for Evidence. What they get off on is not Believing, but in having their beliefs tested. That's why their conversations and their media are so completely dominated by implacable bogeymen: marrying gays, liberals, the ACLU, Sean Penn, Europeans and so on. Their faith both in God and in their political convictions is too weak to survive without an unceasing string of real and imaginary confrontations with those people — and for those confrontations, they are constantly assembling evidence and facts to make their case.

But here's the twist. They are not looking for facts with which to defeat opponents. They are looking for facts that ensure them an ever-expanding roster of opponents. They can be correct facts, incorrect facts, irrelevant facts, it doesn't matter. The point is not to win the argument, the point is to make sure the argument never stops. Permanent war isn't a policy imposed from above; it's an emotional imperative that rises from the bottom. In a way, it actually helps if the fact is dubious or untrue (like the Swift-boat business), because that guarantees an argument. You're arguing the particulars, where you're right, while they're arguing the underlying generalities, where they are.

Once you grasp this fact, you're a long way to understanding what the Hannitys and Limbaughs figured out long ago: These people will swallow anything you feed them, so long as it leaves them with a demon to wrestle with in their dreams.

-Matt Taibbi, "Bush Like Me", Rolling Stone, October 2004