You wrote: "...how people can possibly believe the birth certificate ...that was immediately inspected and determined by every expert who looked at it to be a forgery.
So if I show you an "expert" who looked at it, will you then deny they are an "expert"? You will need some rationale for this contradiction.

http://www.snopes.com/politics/obama/birthers/birthcertificate.asp

and the adobe "expert". 

http://www.foxnews.com/politics/2011/04/29/expert-says-obamas-birth-certificate-legit.html