Either you believe in individual rights or you don't. If an individual can be compelled by the state to admit anyone the state chooses to his business, then individual rights do not exist -- only the collective rights of groups.
To use your example, what IF a black (normal) couple were refused? So what? Let them go somewhere else. Let the business owner suffer the economic consequences of his bigotry (a substantial reduction in his potential market, the resulting public relations embarrassment, etc.). But do not give the government the right to force business owners to accommodate every group IT chooses ...
Once again, the free marketplace is the solution, NOT government.
Not too many years ago, business establishments would sometimes have a sign saying something like “We can refuse service to anyone if we feel like it” but in more formal language.
That is how it should be.
Suppose someone comes to, for instance, a bed and breakfast inn, with 30# of implanted chains, horns, 90% tattooed with profane designs, and so on? The inn keeper should have a perfect right to say “No”. Etc.
There are already laws passed making it a crime to use race as a reason to refuse service. That’s enough.