The counter is why is Obama being held to a higher standard than other white presidents or presidential candidates? Why should Obama have to produce twice the birth certificates as other (white) presidents and presidential candidates? It's insulting.
Asking why Obama didn't show his long form birth certificate earlier is akin to requiring one form of identification, such as a driver's license, when writing a check, but then asking a black person to show a second form of identification (their passport) and then accusing the black person of identify theft for not showing the second form of identification. Finally, when the black person relents and shows their passport, you then accuse the black person of having caused all the trouble by not showing their passport earlier.
I'm at the point where I really do think that the birther nonsense is based on racism. I read an opinion piece that made the point that because Obama isn't white, he has to continually prove that he's good enough to be President. The short form birth certificate wasn't good enough, the long form isn't good enough, his grades are being called into question implying that he got into college because he was a minority instead of on his merits, etc.. Basically, the op-ed's point was that, even in today's society, a black person has to show that they're twice as qualified in order to be accepted and even when 'accepted' their qualifications will be constantly questioned by whites. Unfortunately, I think the opinion writer is correct.