I don't understand why the goal is to "guarantee safety". It seems to be generally accepted that human error causes approximately 90% of motor vehicle accidents [0]. Surely then the goal of any autonomous or semi-autonomous transport system should be to merely reduce that percentage? If all motor vehicles were "self-driving" and the total number of annual deaths was reduced by one, wouldn't that be a good thing? I would rather reduce my chance of dying early than eliminate the possibility of being killed by a bot.

0. http://cyberlaw.stanford.edu/blog/2013/12/human-error-cause-...