But there's two problems here:
1) We won't be replacing all the cars overnight. The problem comes with the interaction between terrible human drivers doing wildly unpredictable, insane things and the inflexible, unadaptable automated cars.
And
2) I'm not comfortable with dying or being injured due to a software error regardless of whether its likelihood is higher or lower. The roads are far more dangerous than the air, and this is why I'm uncomfortable with the whole concept of automated cars on the road and I'm not uncomfortable with autopilot in planes.