He doesn't mass-produce Twinkies for a mass market.

He produces one-of-a-kind custom items for his clients.

If the item they want doesn't jive with his artistic senses or his religious beliefs, he has every right to decline.

If you were a sculptor, and someone wanted to commission you to make a penis from a granite stone, and you refused, would the customer have any right to insist or threaten you with a lawsuit?

What if you are an architect, and someone wants you to design a tree house, and you tell them you don't want to do that.

Whatever "law" you have in mind is not valid and does not apply to custom work.

What ever happened to common sense?