Why are enharmonics not considered to be equal notes?

I have played for several conductors; and one time something really stuck in my mind. One condctor that I had played for became angry because he said we were playing a written A-sharp like a B-flat (he was very rigid in a clical vain). He even said that A# and B-flat are not equal, just as B#/C, E#/F, C#/Db, etc. are not equal. Any thoughts?