That is not the way human beings typically evaluate risks. 'Acceptable risks' are more about psychology and not a statistical calculation. A self driving car that is twice as safe as the human average would be considered an unacceptable risk.
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.
I don't think that human beings factor the rate of injury or death in at all, because human beings are notoriously bad with expected values from extreme conditions.
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.