do you see parents sticking their 6 year olds on the subway just because they can?
Maybe not 6, but certainly 8 year olds are quite capable of using public transport and happily do so in many parts of the world. I know I was taking the bus to the library when I was 8 or 9 and the train into town when I was 10, and that wasn't strange in the slightest.
There's also a big difference between asking a child to navigate public transport and putting them in a trusted taxi to school, which is all an automated car is. If the trusted taxi is cheap enough, you'd only have to be confident that the child wouldn't hurt themselves en route.
I definitely agree with your sentiment, but then I go talk to parents. Parents are protective of their kids. Some are loose, but others are not. I don't have kids, but have worked with them extensively, so I will refer you to some discussions around the issue:
Regarding independence of young children, Penn and Teller did a fascinating episode about stranger danger. http://www.youtube.com/watch?v=IfrSoiaLixg The full episode is on Netflix. You may not agree with all the ideas, but watching the full episode probably won't be boring to you if you feel strongly about this topic one way or another.
Maybe not 6, but certainly 8 year olds are quite capable of using public transport and happily do so in many parts of the world. I know I was taking the bus to the library when I was 8 or 9 and the train into town when I was 10, and that wasn't strange in the slightest.