I do understand what is being said here and maybe I'm coming across as obtuse.
I can see that if you advertise a room for rent then you could say that you are subject to exactly the same rules as a hotel. This may be indeed the "cleanest" way of framing the law.
(A) I don't think anyone would defend a big hotel which tried to ban gays sharing a room.
(B) Also I don't think most people would question the right of a private home owner to have their own rules about who may share a room with whom.
I guess what many people (plus the law of the land as it stands) are saying is that if you let your spare room you immediately go into category A rather than B.
But my own gut feeling (and it is that - it can't be totally rational) is that really it's more like B. After all it is still your home, you are in close proximity to your paying guests, very different from the manager of a hotel where everything is impersonal.
If you have, say, traditional Christian views which inform your everyday life, not just on Sundays, and feel uncomfortable about 2 gays sharing a room, which goes contrary to your religious beliefs does the secular state automatically trump your religion in what is still your own home? Has it in fact ceased to be your home by your letting out a room?
What is wrong ultimately with a couple running a B&B, and advertising it as a traditional Christian house with rules to match? And why would a gay couple, or someone hostile to traditional Christianity, even want to stay there, especially when there are many more establishments around where they would be more at home? Of course if push came to shove, the Christian couple might well get out of the B&B trade altogether rather than go against their own beliefs.
And good riddance, some would say. But it does make me a bit uncomfortable, even though I don't particularly sympathise with old-style Christianity.