First, both homosexuality and pedophilia are forms of sexual immorality - while not exactly equivalent, they are both forms of behavior that Christianity asks its followers to stay away from.
Second, your argument about John Galt is irrelevant and wrong. I did not call Dumbledore gay; the *author* of the books called Dumbledore gay.
If Ayn Rand had identified John Galt as a Communist, then it would be part of "the canon" just as it is now part of the canon of Harry Potter that Dumbledore is gay.