This is mostly worrying about hard to predict second-order effects. Exactly the same problem that caused various health organizations (including WHO and FDA) send misleading messages around corona and vaccinations.
> Issues around who is responsible when a self driving car which is known to be worse than a typical human is deployed, fails, and someone is hurt.
Even if insurance rates would be initially(!) higher than for a regular taxi driver I would expect it to end up cheaper overall and save lives.
Also note that "worse-than-the-old-average" may still end up improving the average because the magnitude by which they're worse is lower. Also, there's nothing magical about "worse-than-average" because for all distributions (except the dirac distribution) there is always some fraction worse than the average, so we always have to expect some fraction of drivers to be worse than average and there's no fundamental reason why they must be human.
In fact, if the fleet of all cars in the world consisted of very safe, very consistently behaving autonomous cars, except for a single vehicle driven by a very conservative human driver who only slowly circles in a fenced private community and never hits anyone then statistically the entire autonomous car fleet may be "worse than average" due to the single outlier.