"I would be surprised if the skies were more dangerous for a drone than the roads for a car"
We have a huge amount of experience with cars and people. We have designed large systems and procedures for cars and people. We are getting some experience[1] with automated cars which is helped greatly by the experience, systems, and rules developed for cars and people.
We don't know the form that automated car deliveries will take, but the unknown distance is from the curb to the domicile. With drones, we have nothing from the warehouse to the domicile and no experience to draw from.
We know what to do in a car crash, I get the feeling drones are really going to go send people into a tizzy. The amount of crap hanging above people's heads is amazing and there is no map to help.
I might be more pessimistic because of the blowing snow outside currently.
1) automated cars in snow seems to be a bit lacking