I don't like the option neither. As stated by the previous replys it wouldn't help much, as every host wants to appear as modern tolerant people, while the reality might be different.
On the other hand, I think this discrimination discussion about refusing certain guests, in general, does not make much sense. I think any host should be completely free to accept or deny a booking request for any reason s/he might put weight on.
Don't get me wrong, please.
Me personally absolutely don't care about the sexual orientation or skin type of a guest and I truly think that discrimination of any kind in the society must be abandoned and it is very very sad, that there exist so much of bad treating of people for racist, nationalist, sex-phobic or any other reasons.
But as a host I want to be free to choose whom I take into my home. I can understand female hosts that want to host only women, for example, and I wouldn't feel discriminated as a man. I can understand a muslim host if s/he only wants to host muslim guests, because s/he wants to share his or her prayers and the rules his or her religion. This is not necessarily a discrimination, but a personal preference about who you want to share your home with.
In the end we preceicely ar NOT hotels, but personal hosts of personal guests and this makes a huge difference.
If I would be guest at a home of somebody who hates what I am and only accepted my booking because s/he was forced to, I wouldn't feel comfortable and I would very much appreciate if s/he would have denied my request.
We could go much further. Do I want a guest who votes for Trump? Hell, no! Hope he doesn't even come close to my neighborhood. Do I want a host who proudly keeps weapons at his home and will talk to me about his heroe state for killing so many in his military service? I'd run away immediatlely. While I absolutely don't care if for his or her love life s/he prefers man or women or transgender or all or none.
From each and any point of view the world is full of a**h**s (the respective other ones), and if airbnb wants to keep the idiots off, it would soon be a very small community after defining who, for the once taken view point, is idiot or not.
I think, airbnb should be open to anybody, even to people who vote for Trump (who for sure at least support any kind of racism, nationalism, religious discrimination and all the bad we know from history). Only criminal people, people acting illegal or people treating their guests bad, should be excluded.
For all the rest, I think personal preferences should be absolutely free and denying of any request should be possible without any need of justification.