>I wish all of these benchmarks pitted autonomous cars against a somewhat comparable user group – say professional taxi drivers – over just a general sampling of the population
This depends on what type of drivers waymo is displacing. If it's displacing mostly professional drivers, then that substitution would be reasonable, because the choices we have are either professional drivers or waymo. However, if it's displacing "normal" drivers, including "first-time drivers, drunk drivers", then the substitution wouldn't be reasonable because banning waymo would mean those rides would be replaced with "normal" drivers, not super-safe professional drivers.
Well at the moment Waymo operates a taxi service, and the only way to use it is as a substitute for Uber/Lyft, so that question answers itself.
Even otherwise though, if at some point in the future I have the option of trading my car in for a fully autonomous one, the only thing I'm really interested in knowing is how my personal accident risk in getting from point A to point B changes compared to if I was driving myself. These benchmarks are meaningless in that regard. I'm not driving drunk, I'm not driving in bad weather conditions, I'm not being needlessly arrogant or reckless on the road. Can this car drive better than me?
This depends on what type of drivers waymo is displacing. If it's displacing mostly professional drivers, then that substitution would be reasonable, because the choices we have are either professional drivers or waymo. However, if it's displacing "normal" drivers, including "first-time drivers, drunk drivers", then the substitution wouldn't be reasonable because banning waymo would mean those rides would be replaced with "normal" drivers, not super-safe professional drivers.