Disagree. If the cake shop is publicly traded, fair enough. If the couple could not shop anywhere else, fair enough.
Otherwise, why do I HAVE to make you a cake? Do you have a right to this cake? Even if it causes me distress? Why is your distress more important than mine?
I would not patronize a shop that made that choice, but I don't feel comfortable taking the choice away just because I disagree with it.
So it would be ok to not bake a cake for a black family because the owner happened to be racist?