To me, the photographer should have prevailed in that case, at least if you believe that portraying a wedding entails personal investment and artistic speech.
As Eugene Volokh and Michael Thomas, both same-sex-marriage supporters, wrote in an elegantly argued amicus brief to the Supreme Court, "photographers, artists, singers, writers, and other creators of expression have a First Amendment right to choose which expression they want to create," and protecting free expression "would not block the enforcement of anti-discrimination law when it comes to discriminatory denials of service by caterers, hotels that rent out space for weddings, limousine service operators, and the like."*
If Arizona was pondering a narrow law meant to rescue any creative professional who objected to any aspect of any wedding from being compelled to invest energy in it, I'd conclude that it was a prudent compromise in a thorny legal area.
That isn't what the state is pondering.
There are two strong objections to their actual effort:
1) The actual text is extraordinarily broad, and would grant religious believers (or people posing as religious believers) far too much special power to thwart all sorts of laws.
Noah Millman adeptly raises this point at The American Conservative:
A properly worded statute not invidiously aimed at stigmatizing gay couples by singling them out would need to allow for general discrimination against any individual whose declared conduct or identity poses a religious objection to the proprietor or service-provider.
This is roughly what Arizona did. Actually, Arizona went considerably further, making an asserted “substantive burden” on an individual’s religious freedom a legitimate defense against individual violations of any state law, regardless of whether it is generally and neutrally applicable. If I understand the law correctly, not only would it legalize a wide variety of types of private discrimination, not limited to my examples above, but would do much more. It would legalize polygamy and marriage with underage girls (both sanctioned by so-called fundamentalist Mormon groups). It would permit public school teachers to explicitly proselytize to their students (I’m quite certain you could find fringe Protestant groups or individuals who hold that such witnessing is mandatory at all times). I’m not sure, but I think if you founded a Church of Nude Defecation, and declared that God told you the Arizona state legislature was your temple, the state of Arizona could not expel you for practicing your faith in the place that God had designated.
Even if the law isn’t quite as nuts as that, it’s pretty nuts. Most people don’t actually want to repeal the process of balancing different interests by making one principle an absolute trump card. They just want to adjust the balance slightly when they don’t like a particular result. Which is completely fine—continual readjustment is exactly what that balancing act requires.
The Economist raises similar points.