We are not talking merely about selling wedding cakes but cutom made wedding cakes. The seller has the right to refuse to design a cake which offends his conscience. I'm sure you will agree that a baker would be quite within his rights to write obscenities onto a cake so if he considers same-sex marriage to be an obscenity then if he refuses to design such a cake he is within his rights to decline. Surely they could take the cake to someone of the same mind as themselves, but that wasn't the object of the exercise, was it?