@badger33 The idea that free speech has some sort of absolute protection even with the first amendment isn't right. 1A only protects against the government limiting speech, first of all. You can prohibit any speech you like in your home, and twitter can limit any kind of speech on its own commercial platform. Even public speech can be limited. Libel. Speech that causes danger (classic fire in crowded theater). Speech that directly incites violence.
@badger33 I suspect that the court would rule based on whether the discrimination is based on what they wanted the cake to say vs. who they are. If the former, probably allow baker to refuse. If latter, then I don't see how they'd justify. Not any more than they could refuse a black-white couple, even if their religion prohibits mixing races.