According to Penn Jillette,  here, commenting on Indiana’s supposedly anti-gay legislation:

These people are not being asked to engage in gay sex or even endorse gay sex. They're being asked to sell flowers and cake to people....Now, I'm a libertarian and an atheist, so I'm kind of fighting myself on this. I don't like the government involved with telling people what to do and I certainly want people to have religious freedom--because the only way that people who don't have religion are going to have freedom is if people who do have religion have freedom. But all the same, we have to be careful we don't get crazy in the hypotheticals. We are not talking about forcing people to engage in gay sex or even endorse gay sex. We're asking that maybe they can treat people the same as other people and that does not seem unreasonable. It's OK, I guess, but goofy to be against gays, but it's not OK to be against people who simply want to...use your services as a business.

Fair enough. They not being asked to engage in gay sex, or even endorse gay sex.

But now, what if instead of being asked to cater a gay wedding, one were asked to cater a swingers' party. (Note: It is irrelevant that swingers would likely not have their parties catered.) Could the same person who is not free to decline catering a gay wedding, decline to cater a swingers' party? Think of it: A caterer who caters a gay wedding because not to do so, by virtue of being discriminatory, would be illegal, can turn right round and refuse to cater a swingers' party. How could this be? After all, these people are not being asked to swing themselves. Moreover, they may not even see the swinging.

What if, nevertheless, a caterer has a religious-moral objection to the sort of activities in which swingers engage, the same sort of objections he or she may have to gay weddings? That is, it conflicts with the sexual ethics of one's worldview. Apparently, one's religious-moral objections to swinging would be an acceptable basis in the law for refusing a request to cater such an event, but those same objections to same-sex marriage would not justify turning down a request for catering services.

Remember: No one is asking a caterer to swing with the swingers. No one is even really asking that a caterer even see the swinging. No one is asking a caterer to approve of swinging. To paraphrase Jillette, caterers are only being asked that maybe they can treat people the same as other people. That doesn't seem unreasonable. It's perfectly fine, if not a little goofy to be against swingers, but it's not perfectly fine to be against people who simply want to...use your services as a business.

Needless to say, the same goes for a photographer or anyone else whose goods and services may be desired by the swingers, again with the stipulation that these purveyors would not be participating in or even seeing the swinging as it takes place.

All of this is less than academic because this furor isn't about rights or discrimination anyway. It's about other things.