The gay marriage side of this is a complete straw man. In a free society, a private group has every right to refuse service for any reason. It has nothing to do with discrimination and it's definitely a case the government should be siding with the bakers.
I support gay marriage, but I also support this couple's decision. To support otherwise is supporting the removal of individual freedoms.
The stance that "a private group has every right to refuse service for any reason." is the same thing that they said in the South with Jim Crow laws and racial covenants. So how can I say that what the couple is doing is within their rights but at the same time say that Jim Crow laws were not right? I can't quite square that circle.