Humans have only two eyes and terrible reaction times. They also get distracted easily and tend to act emotionally often. There is little data to show that computers are better drivers, because currently they aren't, but they lack human weaknesses and are safer than humans in many other situations (planes, trains...).
While computers lack human weaknesses, they bring a slew of new ones. Computers have no situational awareness, no context, are vulnerable to hacking, respond in predetermined ways which can be manipulated or abused, etc.
There just is not enough evidence to make the claim that ubiquitous autonomous cars will be any safer than human drivers on shared roads. There are many known unknowns and who knows how many unknown unknowns left to discover and mitigate with this tech.
But also computeres are easily being possessed by WannaCry and other malicious activities. It is pretty sad that all the praising of AI doesn't take into account the adversarial nature of the World.
