For the same reason I don't like being called Japanese. Or why I don't like being called Itallian. How about being called a girl? Or being called a cat?
I don't like being called gay because, I am not gay.
If I were not Goth, would I want to be called such?
If I were gay, then I would not want to be called hetero.
I hope this simple explanation helps you understand that most of us are far from homophobic. Perhaps we are stereophobic (new word:P)