While this is indeed a terrible thing, I fail to see a strong correlation to the fact that the attacker entered the building due to the keys being at the counte

While this is indeed a terrible thing, I fail to see a strong correlation to the fact that the attacker entered the building due to the keys being at the counter. That is a possible reason along a million more, such as the fact that the attacker could force the door's lock, get someone else from the building (an accomplice?) to give him illegal access. Pointing the blame at Airbnb therefore feels odd. Things like these can also happen (and they do, probably even more often) at your own place, and would you sue your landlord if so? Whether these things are more probable to happen at Airbnb is also a very hard thing to prove. IMO your own place might be riskier as an attacker can study your routine over time, which opens up more security holes. These type of attacks are probably outside anyone's control and I don't think the Airbnb places have an implicit responsibility to ensure a higher level of security than you have at your own place (it can be a Airbnb luxe feature, though?)