This makes me uncomfortable. As much as I would prefer that bakeries not discriminate, I don’t like using the law to compel them to, both from a political perspective and from a legal one.
Politically, I think it’s a mistake. The argment for allowing gay marriage has long been that gay marriage has almost zero impact on straight persons. If you don’t support gay marriage, then don’t marry someone of the same sex. And many, if not all, conservatives understand that — especially in more libertarian areas. Gay marriage doesn’t change the rules for straight marriage. It doesn’t compel the clergy to officiate at gay weddings or live with a gay roommate or even be polite to gay people. But … now you can be compelled to bake a gay wedding cake. And that complicates the libertarian case for LGBT rights.
It also comes across as spiteful. Unless you think unhappy bakery owners make your wedding cake more delicious. Salty tears and such.
Legally, there’s a First Amendment issue, but I think the ultimate outcome will turn on the facts. Now, the argment for why this is permissible generally goes: “Cake baking is commerce, not speech. It’s the same justification for why Congress can make it illegal for restuarants and shops and so forth to discriminate based on race.”
That distinction between commerce and speech is tricky though. While it means a book store can’t refused to sell books to a person of color (commerce), it does mean that a book store can refuse to publish, endorse, or (maybe) even offer for sale books books featuring protagonists of color (speech, association). Likewise, while the state might be able to require that a bakery serve both straight and LGBT customers, there’s a limit to how much it can compel the bakery to “edit” its cakes to fit the needs of LGBT persons (at least to the extent that cake is considered speech).
That is, if you sell pre-made cakes in a box, then your First Amendment case is pretty weak. But if you customize your cakes based on how you perceive the couple, then you might have a case.
Either way though, this case definitely rubs the spirit of the First Amendment the wrong way. My First Amendment gut check involves replacing the “good guys” in any scenario with Neo-Nazis and seeing how I feel about that. And here, that means it would be permissible for the state to compel someone to bake a birthday cake for Hitler. As I said, that makes me uncomfortable.