My question - would you rent out a room in your house for a night if someone starts leaving crappy reviews about you everywhere? Many people would not.
I think Airbnb AND homeowners should carry much more liability for some of the fraud on Airbnb, so I hope to see airbnb paying big penalty bucks in the future.
Airbnb likely dislikes third party reservations, offsite payments and offsite bookings for business reasons as well. I wouldn't be surprised if folks going off-site are asked not to participate on-site - fair or not.