I think the first confusion here lies in equating baking a wedding cake for a same sex couple with doing something immoral.  Even if you believe homosexual acts are wrong, even if you believe same-sex marriage is wrong, baking a cake for a homosexual couple is not immoral, even a wedding cake:  It's just baking a cake.  If you're already in the business of making wedding cakes, it's what you do.  You're not approving of any particular marriage, or sanctifying it---You're just providing a service.  

I believe the error arises because of people like Minnery, who want to make a case for asserting religious beliefs in the public sphere, and that the issue of "religious freedom" itself is a trojan horse for political and social transformation in the name of religion.  It's not just cakes:  Sooner or later it'll be vital services, other religions, and deja-vu all over again