First off Musk made a really big mistake IMHO calling the software "Autopilot". It gives people with too much trust in the system a false sense of security. It's a highly advance driving assist program like every other one currently available. It can be a life saver in certain situations but is still not a complete substitute for a person behind the wheel.
The big problem is no software is 100% bullet proof 100% of the time. No matter how well coded and debugged there are edge cases where it will fail. With something as complicated and potentially erratic as driving a vehicle, it's fool hardy to leave it totally in the control of a software system, period.
The only way to make self driving cars close to 100% safe is to reduce the complication and erraticness of driving by making everything self driving, or completely separating self drivers from human operators. With that said driving assist systems with a driver properly monitoring have the potential to reduce accidents by a highly significant amount, and shouldn't be discounted out of hand.