To clarify my original post, it is not that artist can deny service to selected people, but can deny to use their art to express beliefs the artist doesn't believe in. For example, if you're a Christian jeweler, you can't deny services to any person who wants you to design a diamond ring whether they're LBGQ, a minority, or a believer in witchcraft. However, if they want you to design jewelry depicting some witchcraft motif, and that offends you, than the constitution protects your right of free speech and expression.
So I would think that let;s say a wedding photographer cannot deny a gay couple from hiring them to shoot a birthday party. But if the photographer doesn;t beleive in gay marriage, the consitution protect their rights of expresssion and free speech and doesn;t have to shoot the gay wedding. A Jewish cook can refuse to prepare non kosher meals. A vegetarian caterer doesn't have to serve meat. etc.
This right of free speech does not extend to businesses like hotels and restaurants open to the general public to deny minorities, LGBQ, or anyone else.