If the gay couple is asking for a wedding cake in the shape of a dick, then sure... artistic reasons for declining that sale.
If the gay couple is asking for a wedding cake that looks and tastes much like any other wedding cake, then no artistic reasons for declining the sale, IMO.

Just like you can't refuse to sell things to Mormons or to Christians. Allowing that kind of behavior foments a culture war. It is antithetical to a society of free people, free to live and love and worship as they please without fear of being denied common rights when they are in a public space.

You defending the rights of a Christian to deny service based on faith is equivalent to arguing that it's legal to deny Christians service based on their faith. This policy pushes Americans into their little cults, it doesn't unify us; it divides us.

The notion that a gay couple marrying is an affront to anyone is total BS, anyway. The Bible mentions gayness maybe - MAYBE - 3 - 4 times, and at least one of those is in Leviticus. LEVITICUS! Go ahead and read some of the verses from leviticus and tell me any of that has any bearing on modern life. "Thou shalt not wear clothes of multiple fibers" or some shit is in there. Well... damn us all to hell for our cotton-polyester blends.

Whereas the Bible, in no uncertain terms, says that divorce is a sin against God like over 100 times. So when someone gets all frothy at the mouth over the Bible telling them gay is the bad, I can't take them seriously unless they're on a personal crusade to outlaw divorce.

Plus - Christianity teaches to reserve judgement for the lord, and to turn the other cheek, and to be a 'good Samaritan.'
So tell me how sticking it to the gays is upholding Christian morality, again.