This is getting even weirder. Every wedding cake is personally constructed. The personal constructor is called a baker. The gay customer comes into the shop, says he's after a cake for a gay wedding, points to the picture of the cake he wants, holds out the cash.
Can your baker provide the cake?
What about this scenario: most supermarkets including the one near me create cakes that can be purchased from the shelf. i.e., it is a cake that has been baked (personally constructed) and is available for purchase.
Now: a gay couple comes into the supermarket, sees the cake on the shelf, and indicates it would be perfect for their impromptu wedding. They are about to take the cake when out of nowhere, a screaming Christian banshee comes out of the bakery telling them they are sinners and cannot purchase that cake since its usage in a gay wedding would be an abomination to the baker's god. And the baker snatches the cake from their hands.
The manager of the store comes over to see what the commotion is about, reviews what has transpired, and now has two options before him/her:
Option 1: Indicate to the gay couple that he/she has to respect the poor persecuted Christian's batshit sensibilities and has to respect their religious views and thus indicates the baker was in the right for their behavior.
Option 2: Fires the batshit baker, apologizes to the gay couple, hands them the cake, and tells them to have a nice day.
Then again, perhaps my scenario is unlikely in light of the following: