I think they may need to make the service about the physical place, and about customization. If a person can take a regular retail products from vendor door to their door, and they order a product that is offered to anyone that walks in the place, don’t deny them. If they want you to go set up some extravagant cake at a gay wedding, or attend and photograph one, that should be at the discretion of the vendor.
But all of this is fake. These are loony activists that just want to find any way they can to harm a person that disagrees with their deviant life style