Driving is inherently very dangerous. Traffic accidents are a leading cause of death in the US. You're not really chasing perfection to win this game. It's not all that hard to beat humans on average, because the average human is pretty terrible. It's a statistical certainty that some people will die at the hands of Autopilot even when it's in some final non-beta state, but it will probably be less people than would otherwise die to the same miles driven manually.
The hard thing for Autopilot-like systems is perceiving the world accurately. "The world" includes both the physical reality of roads+cars it senses, as well as things like traffic rules, corner cases (construction, debris, manual police control of an intersection with a dead traffic light), and gauging the intent of other/human drivers. Humans are inherently better at that stuff. The software has to get better than it is today, but it will probably never fully match the best humans at this part.
However, there are two key ways the software inherently outdoes humans:
(1) It can have more sensory data than humans. Even Tesla (currently sans Radar + Lidar, just cameras) can see in every direction at the same time, all the time, with an overlapping array of cameras. No blindspots, no temporary blindness in one direction while you crane your neck to check in another, etc.
(2) It never gets tired, distracted, or drunk. It's never checking a facebook feed, or nodding off after a sleepless night, or too engaged in a conversation with a passenger to remember to look for that cross-traffic, etc. This is a huge advantage when it comes to accident rates.