A)
If a gay couple entered the bakery in order to purchase any other product (something that isn't to do with celebrating a gay wedding), would the baker decline to serve them?
B)
If a heterosexual Christian personal friend of the baker's (who attended the same church) came in and asked for a gay wedding cake, would the baker make an exception and serve that friend? Would the baker say, "I normally have a principle against making cakes for gay weddings, but for you, I'll do it"?
What am I trying to illustrate? That it's not about the person(s) being served, but it's about the service that the baker is being asked for.