I am also uncomfortable with this. We once had a guest trying to book with us and his profile picture was him in a harley jacket downing a bottle of jack daniels straight from the bottle! Needless to say this threw up some red flags. However not showing the profile pictures may have something to do with AirBNB's non discrimination policies.
The best thing you can do is only allow guests to book that have a governement issued ID, even then I'd prefer to attach a face to the name. I don't trust people as much that don't have their profile picture of themselves or publicly visible.