Sure, we can use subtle hints as to determine rather or not Madara possess Amaterasu.. However most members want hard evidence in which we really don't have other than the fact that Kishimoto has proclaimed that Susanoo=Amaterasu, and Tsukuyomi..
What I'm getting as it if Madara hasn't shown Amaterasu then most members won't believe he has such a technique which is futile to argue against until he(hopefully)shows the proficiency in knowing such a technique.