It's a union thing. In NYC, the L service is completely automated, but the union won't let trains run without two crew members. It was apparently hard enough to get the union to allow the G line (the least popular line that only runs half-size trains every 20 minutes) to run one-person operation on the weekends!
(Though if you don't need drivers, why do you care about the union? I guess the problem is that it will take maybe 50 years to convert the other lines to automatic operation. And you still need someone on the train to answer rider questions and handle medical/police issues.)
Is this an argument that a human driver is required? To me, it sounds like if there's nothing you can do, the computer's job is much easier, not harder.
Unlike humans, computers never get tired from working long hours, can see around corners using various sensors and process the information fast, and can act immediately on instructions from a remote operator.
