Add something that is new/unknown + lack of control, and you will have to clear a very high threshold to be considered 'acceptably safe'. My guess is a minimum of a 0.1x.
Once people get used to taking robotaxis, they won't care. The bar is "safe enough for very few people to have a bad experience." If you take 10 robotaxi rides in a row and they all go flawlessly your subjective interpretation of the risk will be that there isn't any.
I feel confident saying this because if you die in the US to anything other than old age, it was almost certainly a car crash. Despite this, most people don't think twice before getting in a car.
You and I are thinking with a purely logical thought process, but most people don’t reason that way.
A lot of people want to be able to hold someone accountable, and that is more important than the pure probabilities.
They want to be able to blame a person for making a mistake.