The thing is these are not the "absolute worst-case human driver", these are the absolute average human drivers. People get easily distracted, get excited, get

The thing is these are not the "absolute worst-case human driver", these are the absolute average human drivers. People get easily distracted, get excited, get tired, all of which are propitious to bad decision-making. Many human drivers are downright dangerous, but that's not a reason to add dangerous machine drivers on the road, either.