Why do you assume "properly licensed" drivers will be better? My driving test in the United States was a joke. Many are the same. Nothing about it prepared me to be a good driver (which I am not). To me, the phrase "properly licensed" means nothing more than I hold a small card in my wallet that say I am allowed to drive this car. It says nothing about my skill level.
If your skill level is too poor, you get your license taken away.
I disagree. Some people will drunk drive no matter the legal consequences, or in my case, I once rear-ended someone because I was drowsy but kept driving because I wanted to get home (fortunately no one was hurt, and yes, the accident was completely my fault). The comparison should be against the general population of human drivers because that's the reality on the road.
You really think the safety bar for running a commercial autonomous taxi service should be set lower than the average human legally entitled to drive!?!