It wouldn't necessarily. Perhaps figurines. But does the content need to change? Wedding cakes are personalized orders.
The bottom line is, if the refusal hinges on the identity of the couple seeking services rather than some tangible distinction in the work product, the bakers would potentially run afoul of civil rights legislation where sexual orientation is protected.
Some believe that the act of baking one for a gay couple's wedding is an expression of approval.
...while others believe that allowing that couple to walk down the street unharassed might also be a sign of approval.
I guess I just don't know where this would stop. It is generally established that civil rights legislation can mandate equal access to public accommodations, thus if you deny access to a gay couple on the basis of who they are, you are denying them a recognized right. If civil rights had yielded to any purported religious freedom no matter how vacuous in the 1960s, the civil rights legislation would have failed at its primary aim.
You seem to be saying that a business can't be made to express something that goes against their beliefs but then define for them what defines 'expression'.
Well, I'm willing to say that it can't be nothing. They have a burden to prove before they even have a case to be allowed to truncate the rights of other people.