Why don't you think that a man aspiring to the highest office in our land should prove who he is?
It could be, unlikely as it is, that Obama has provided such proof to the appropriate officials and that he's simply too stubborn to give in to the clamor.
On the other hand, I haven't seen any compelling argument with documentation that proves Obama is not a U.S. citizen. For example, receiving an Indonesian passport doesn't extinguish American citizenship, which is regulated by U.S., not Indonesian law.