Even though I view Mr. Phillip's personal beliefs as ignorant, narrow-minded, and primitive, I have to agree that he should have a choice what artistic projects he decides to work on (but only as a small custom shop). As an agnostic and freelancer, I wouldn't want to be forced by law to work on Christian music, though I probably would if the pay was fair and the client was friendly. 
I say let the cause and consequence dictate how his small business (as a freelance artist) behaves. If he wants to discriminate against certain people, that's his business; go elsewhere and leave it to Karma (or whatever) to shut him down (or not) eventually. 
However, when it comes to large corporations who have a monopoly on things, or even just grocery stores, gas stations, companies that deal in things that everyone needs, etc., that's where the law should step in. If there was only one giant food company for everyone (which would be terrifying and dystopian) discrimination would be fatal for many.