Social issues can at times work to your advantage, take the recent protests and support for
Chick-fil-A for example. But it can also be your detriment, as I recall reading about a lawsuit involving a photographer recently, because they refused service to a same sex couple.
There are always moral issues at work in business. Do car salesmen wonder if their customers are drunks who could potentially run someone down with the car they're about to sell? Do gun shops feel remorse when one of their customers commits a crime with a weapon they sold? Does Wal Mart enable drug users by selling bath salts?
Small business owners can't really afford to picky. However, we'd all better consider the ramifications of our actions on our reputation, which in most cases is even more important than the quality of our photos. This is a referral business after all.
Sure, refusing service to a gay couple might win some points with the blue haired ladies in your local church group, but who are you alienating in the process? It might be a young mom with 3 small kids who could be using your service for the next 15 years...and she's a vocal member of the PTA with a large circle of influence.
Being just a wedding photographer is saying enough, in my opinion. If you try to niche your way into the gay market, the risks far outweigh the rewards.