From the e-mail I received yesterday it's also not clear what happens exactly when you don't sign:
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What if I decline the commitment?
If you decline the commitment, you won’t be able to host or book using Airbnb, and you have the option to cancel your account. Once your account is canceled, future booked trips will be canceled. You will still be able to browse Airbnb but you won’t be able to book any reservations or host any guests.
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So it seems that if you decline then you can still host the existing bookings that you've accepted. It does not mention this specifically and immedeately begins about account cancellation, which would clearly cancel your existing bookings and inconvenience your booked guest.
Has anyone seen the exact final text though? It's not difficult to accept to not discriminate based on ethnicity, gender, etc. It only gets complicated due to AirBnB's insistence on conflating it with that InstantBook feature. (So just signing the agreement in itself isn't actually all that controversial IF it's actually an anti discrimination policy without any business policies mixed in.
If it's ACTUALY just the following (also from that e-mail) then that's a complete no-brainer to accept:
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What is the Community Commitment?
You commit to treat everyone—regardless of race, religion, national origin, ethnicity, disability, sex, gender identity, sexual orientation or age—with respect, and without judgment or bias.
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The above doesn't even state that you can't decline a person from a particular country, it just says you have to do so respectfully. (I can't imagine that being the case though. That email raised a lot more questions than it answered.)