We're not talking about an incident where someone is kicked out of a restaurant for skin color (NOT a recognized religious tenet of any faith I am aware of), we are talking about requests for events supporting a holy sacrament.
One cannot and SHOULD NOT be required to set their faith or beliefs at the door because they are engaged in commerce.
And if you ordered a cake with white frosting saying "Congratulations," it might be just fine and dandy. But, when you are ordering a cake that says, Happy wedding day, Bob and Steve," it can cause a conundrum. Most bakers aren't going to inquire as to the reason for the cake, but a message on the cake - perhaps even producing it - may very well conflict with a strongly held belief and they should not be forced to participate in something that can be seen as supporting the act.
We are swiftly moving to a point where even speaking against same-sex marriage will be seen as hate speech. It's already happened in Canada and Great Britain, and on US college campuses, and religious organizations that hold an opposing view to same-sex marriage are branded as "hate" organizations in the same breath as ****s and other white supremacists. However, until that time, people should be free to act on their conscience and not compelled through the power of the state to conform. If it is a poor business decision NOT to bake cakes for same-sex marriages, then let the marketplace decide - not the state.