This issue has pretty much already been decided ... back in the 1960s ...
You cannot refuse service to any patron based on race. Race is a characteristic of birth it is illegal to refuse service on the basis of race. Homosexuality is widely accepted to be a trait with which one is born, equivalent to race. Therefore, discrimination an the basis of sexual orientation is equivalent to discrimination on race, illegal.
You can argue about the morality of the homosexual sex act (just as you can argue the morality of the heterosexual sex act), but you can't discriminate or refuse service to a person based on his declared sexual orientation.