For the most part Americans have a strong reaction when civil rights appear to be violated. If nothing else, most of us stive for fairness. In the case of the cake decorator who refused to decorate a cake for a same sex union, whose rights are being denied, the customer or the baker.
You didn't see that coming, admit it. When we demand, there is a good chance someone is being injured. The obvious point, whose rights are more relevant the marital couple being denied a cake, or the baker being forced to make a cake. I say you can choose not to bake.
However, this case is precisely why we need wise men and woman to hear cases and render decisions. My Libertarian leaning brain tells me there is no reason to compel an individual cake maker to bake when there are dozens of oven masters willing to provide said service.
There are also "self-evident" cases" where one is competing for housing and is denied the comfort of a roof over one's head on the basis of race, creed or color. I would argue from the point of view shelter is a basic need and of course cake is just comfort food.
Back to my civil rights argument, we do tend to violate civil rights when convenient. For example, in King County Washington the outward public display of a Christmas Tree or Menorah is considered an overt offence to those who don't like Christian or Jewish symbols. So, bring it full circle, the government is allowed to violate Jewish and Christian rights. King County does not seem to mind that infringement on the season to be jolly. Last check the Hammer and Sickle is still ok.