That puts an unreasonable burden on the baker though. And the gay couple didn't give a damn about a wedding cake that they could have gotten a dozen other places. The intent was to hurt a Christian baker. I don't think a Bible verse would have deterred them from that in the least.
Bottom line, a proprietor should have full ability, with no issues from anybody, to choose what legal products he/she will sell, what creative content he will provide, and should have complete ability to refuse to carry any other products or provide any other creative content.
I loved Task's analogy, i.e. forcing a Christian baker to accommodate a gay wedding is no different than requiring Hillary Clinton to give a pro-Trump speech at a conservative Christian or gay gathering.
I doubt any leftist here would suggest she is discriminating against gays or blacks or denying them their rights if she turned down that invitation.