I'd been meaning to write about this for a while -- and, once again, I'm late to the party, killing my ability to write clever comments on other, more popular, bloggers' posts with a link to try to drive traffic here. Which, I'm not ashamed to admit, is the primary mechanism a new blogger has to try to build a readership.
Anyway, there are a large contingent of commenters, bloggers, pundits, legislators, and judges for whom the issue is simple: providing a service such as wedding photography, cake-baking, catering, reception deejaying, or even providing a wedding or reception venue itself, is a public accommodation, and thus refusing services to a gay or lesbian couple is every bit as wrong, and illegal, as denying such services to an interracial couple, and just as wrong as it was for lunch counters to serve blacks in the pre-Civil Rights South.
First of all, the services surrounding weddings are all very personal services, requiring the service provider to convey a fair degree of enthusiasm towards the wedding itself, whether it's coaxing a smile out of a nervous couple before taking the photograph, or enthusiastically greeting them as they enter the reception ("Please welcome the new Mr. and Mrs. Actuary"), a successful service provider is obliged to celebrate the wedding rather than fairly impersonally provide a service. True, a wedding cake or flowers are more impersonal, but I would still imagine that at a mom & pop store, the requirement to share the celebration is still there, where in a corporate environment where a cake is selected over the internet, it's not. Hence, it is undeniable that to require someone to provide these services requires them to endorse the pending nuptials.
(Could a service provider simply grit their teeth, provide the service, and do a crappy job at it? Not likely. A grumpy photographer simply isn't doing the job the couple is engaging them for -- they're being paid to be enthusiastic.)
Second, the belief that a marriage, and parenting, should be reserved for opposite couples, is not an opinion borne solely out of animus towards gays and lesbians. There is a legitimate reason. It comes from a belief that children deserve to have a mother and a father, and is part and parcel of a moral structure in which sex and children are linked together, and a part of marriage. This simply can't be equated to racism, which has no connection to a wider moral code. Gay marriage supporters may reject this moral code, just as "open marriage" supporters reject the requirement of sexual exclusivity, but they shouldn't deny the right of others to hold to these beliefs.
Third, in the case of Jim Crow, blacks suffered acutely from the segregation they experienced. Families travelled with the "Green Book," a guidebook which provided them with listings of the small number of hotels and restaurants which would open their doors to them. And wasn't there a scene in the Ray Charles biopic in which he and his band couldn't find places to stay, or places to perform, as they travelled the South?
This is not remotely the case for marriage-service providers. Instead, in the New Mexico case which has been featured in blogs, the lesbian couple acted as a "tester," with the two women contacting the photographer separately, in the one case explicitly mentioning it was a gay ceremony, and in the other not, to determine that the photographer denied them due to the fact that it was a gay marriage, and not for other reasons. (Note that the link doesn't describe this; it was the first hit in a quick search, but I had previously read about this more extensively.) In no other case that's surfaced have I read that the gay or lesbian couple could not find a service provider, or had any difficulties at all, since there are plenty of photographers, caterers, bakers, etc., and only a small minority who would be imagined to decline gay marriages under any scenario. True, they were rejected by their first choice -- but what engaged couple gets a price quote from only one service provider, rather than pricing out multiple photographers, and the like, anyway?
The "no discrimination in public accommodations" advocates insist that, even though no real harm is caused, the principle of the thing requires that all such service providers be open to all. This is the key: this is a case of balancing rights, not of exercising a right absolutely (as with employment, for instance), so whether there is demonstrated harm does matter.