I think the answer is "quite paranoid" -- here are a couple possibilities I think are more likely than yours:

- Early adopters were less likely to vandalize apartments, so as AirBnB becomes more mainstream we will see an increase in vandals.

- Criminals are starting to realize that AirBnB lets them get around mandatory hotel registrations / ID checks

- AirBnB hosts, having had many good experiences, have become more lax than they previously were in their screening/supervision of guests.