The issue of a photographer saying no to a gay couple vs a restaurant / retail is that in the case of a restaurant/retail the owner is simply providing a service they do to everyone else. (Serve food, sell shoes...) For a photographer you are not just selling prints. You are forced to attend a religous ceremony which goes against your beliefs. In my mind if a photographer who is clearly against gay marriage (Which i am not. I fully support everyones rights), if they were to not sell some of their artwork to gays that would be wrong, but to refuse to attend a wedding would be justified. Certainly in those states that allow gay weddings, they do not force the priests to perform them do they? This of course would apply to any profession that would attend the wedding. (Musician's doing the ceremony, priests, photographers, videographers....)