Also the important issue here is not just the (terrible) handling of this specific incident by Airbnb but the fact that it puts into question their entire business model: Is it really smart to rent out your personal residence to a complete stranger? Does the potential benefit($$$) outweigh the significant risks(being completely violated)? Yes, they could put in some more checks but will that be enough to make people feel SAFE?
Personally I think the risk is too high and the problem will only become worse as the service tries to expand to more customers and scammers become more aware of it. That nice "guest" may simply be casing the joint, copying your keys and snooping in your mail. Who needs that risk?