i think a business owner should have the right to refuse service to a client. i have owned a few different businesses over the years and have exercised that privilege on occasion, all for different reasons. mostly because the client did something along the way to make me uncomfortable to trust them to pay me or treat me decent. never was it over someones religious, political, or social views. i always tried/try very hard to remain sterile with my clients so i don't learn too much about them personally and in the south that is kinda hard. people here want your first born before they do business with anybody.
one last thing...i research who i do business with because it is important to me to know where my money is going. i think that sucks that happened to that couple!!!