Autonomous driving doesn't mean, that the car can drive by it's own, but it's a security feature which helps to reduce the accident rate. In cars from the past, only the human driver is in charge of adjusting the speed. The result is, that sometimes, the human are overestimate their ability to handling the sky and they drive in the urban area faster than it's allowed. A crash with other vehicles is the result.
Self-driving cars are monitoring the current speed, and compare the value with the allowed speed. This allows to give feedback to the human driver. That means, the car recognizes if the human driver is too fast and can ask him to reduce the speed. This won't prevent any mistake, but it helps to educate the person behind the wheel.
If somebody is an expert driver he won't need a self-driving car. But if the driver is not familiar with driving at all, it make sense to use the additional help of a computer-based tutorial system. It will tell the driver what the correct position in the lane is and what the allowed distance to other vehicles should be.
The disadvantages of self-driving cars is, that the feature is very expensive. To provide the mentioned guidance a lot of cameras and lidar sensors are needed. Additionally, a full blown onboard computer with the ability to interpret the raw data in realtime needs a lot of energy. Only expensive cars are equipped with such capabilities. The question for the engineers is how to reduce the overall costs, so that a driverless feature can be realized in any car on the market.
The surprising fact is, that an autonomous car without a human driver doesn't make much sense. Because the car knows already what the allowed speed in a city is. The bottleneck is the human who doesn't know exactly how fast he is allowed to drive. Instead of driving a self-driving car alone, the better idea is to invite 3 friends to attend the car, because they can be educated as well. A self-driving car is some kind of mobile driver school in which the humans in the car can discuss which kind of behavior is right.
Has the overall society a need for educating humans in driving? Yes there is a demand. Most of the 1 million driver accidents each year are the result of human error. That means, the driver behind the steering wheel are not familiar with the traffic rules. They were driving too fast, the distance to other vehicles was too slow and they doesn't see the red traffic light. If the human drivers are educated much better, the vision zero can be realized.