He had baked them cakes before so the denial of service was not based on who they were.  It was the type of cake that was asked for.   Would you insist that the baker make a cake in the shape of a woman's breast or one that had the n-word on it if they were requested?  Or how about one that said 'whites only allowed'? Or something else derogatory?  Plus, there is a practical side to this.  If you force somebody to do something like this, how do you know they will do a good job?   For all you know, they will frost over some mud or something else and you will never know until you try cutting into it at which time it will be too late.