There are no scientific reasons the world can't chart a path, albeit a difficult one, toward the world's first AIDS-free generation, a top federal health official said Sunday. "There is no excuse scientifically to say we cannot do it," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, speaking to the media at AIDS 2012, an international AIDS conference, which began here Sunday. "What we need now is the political and organizational will to implement what science has given us."