The legal merits aren't what I want to focus on. Rather, it flows out of a sub-issue that sprang out of a commenter alleging that very few people "would (dare to) take the photographer's side here if she refused to photograph a mixed-race couple." Volokh responds:
I should hope that virtually all of those who support Elaine Huguenin's Free Speech Clause rights would support that hypothetical photographer's constitutional rights, too. I certainly would, just as I support the constitutional rights of many people whose views I condemn.
When someone is discriminated against, the harms of that act are twofold. First, they are denied whatever benefit or opportunity that was being putatively offered -- in this case, having this photographer take pictures of a wedding. Second, they are faced with the stark and bald assertion that they are -- from the perspective of the discriminator -- a second-class citizen, one whom is particularly unworthy of her association or services.
Both of these harms can be remedied by law or by society. Law remedies the first by mandating the performance of the service. It remedies the second by sending the message the political community does not acquiesce to the assertion of inferiority. Both of these roles are important functions of anti-discrimination law.
Of course, sometimes it is not appropriate for law to intervene. Perhaps (as might be the case in the New Mexico controversy), the discrimination is intimately connected to another important right or principle, which the state must also be respectful of. In that case, society can also provide a remedy for both of the harms of discrimination. For the first, the couple can simply find another photographer. And for the second, society's expression of outrage and dismay can also send the message that the discriminated-against party really is to be included on full and equal terms, and it is the discriminator who is the outlier.
Often times, this expression of outrage occurs in tandem with the assertion of a lack of legal jurisdiction. "I condemn what you say, but defend your right to say it," as the saying goes. Volokh also makes note of this, condemning the hypothetical racist photographer while still asserting he would defend it. The availability of this sort of social sanction is, I feel, one of the ways we rationalize the withholding of legal remedy to many victims of discrimination.
But, this assumes that social sanction is, in fact, available. And for many gay and lesbian Americans, it is not. They are in a position of extreme vulnerability compared to, say, mixed-race couples, who can count on public outrage if they are discriminated against. Hence, they are even more reliant on legal remedy than many other groups. But of course, the fact that they are relatively more marginalized (that the question of their public equality is more controversial) makes it far less likely that law actually will protect them.
I've already noted the existence of this double-bind -- that law only protects minority groups who have displayed some measure of political power -- in the context of gay Americans before. In a sense, it merely states the obvious: it sucks to be marginalized, and the more marginal you are, the suckier it is. But it is important to note the extra layer of vulnerability that certain groups face when they can't count on extra-legal statements of support and affirmation in the face of discrimination. When the response to discrimination is not "I condemn but I defend", but "I defend and they're damn right to do it, too," the harms of exclusion are amplified dramatically.