This is one of those things that always struck me as a weird, poor argument... how is autonomous driving supposed to suddenly make everyone want to stop owning their cars and use taxis instead?
Ignoring the driver, taxi/ride-hail/autonomous-ride services are much more efficient uses of a vehicle over time. (And this is just a side note, but obviously if you don't have to pay for a human driver, you make the cost of operating the vehicle much lower per kilometre, and then it becomes much more attractive, from a purely financial POV, for most people than owning their own vehicle.)
If you are ready to wait for a car to come pick you up, or to plan your trip based on the schedule of the car, and to pack your stuff in one bag that you can carry along...
... then, my friend, you are ready for public transportations :)
Car sharing is inconvenient because you first have to get to the station. Public transport often doesn't take you where you actually need to go, you're stuck to a schedule, you can't transport anything big, and it's often slower than a car. Cheap robotaxis fix that.
More importantly, I think many people have a car because there are some trips that just aren't realistically feasible without, and then they use the car because they already have it, have paid the fixed cost, and it's marginally better than public transport. With cheap robotaxis, they might use public transport for 90% of the trips because now they don't have to choose between owning a car and being unable to do those remaining 10% of trips.
Where I come from (not the US), in cities you have a bus/tram/metro every 5-10 minutes, bringing you everywhere, for a fraction of the cost of an Uber (which is why nobody uses Uber).
Places that don't have good public transport are quite remote, usually there are no Uber there, and if there is a taxi service it is quite far away so you have to wait and it's expensive.
Finally, moving one person at a time in a big heavy vehicle is less energy-efficient than having them in public transport (or better: taking the bike!). So public transport + bike again wins there, I think.
But again, it depends on the quality of your public service.
I don't go on a lot of long-term trips, but if I did that would still be a reason to get one car for a household instead of multiple. For rarer trips I would be happy to have a rental drive itself to my house.
If you mean day trips, then none of those issues are notable with a competent self-driving fleet except "one bag", but I don't think I've ever needed more than one bag for a day trip...
People that live in cities, where this is most likely to catch on earlier, already can't leave anything in their cars unless they want to come back to a smashed window.
in cities where the public transport sucks, you mean? I just don't understand who would ever want to use a car inside Paris or Amsterdam, for instance.
Already many people would benefit financially from using public transport or ride-sharing, or even carpooling, but they don't. Because they want their car! Many people are paying too much to fuel up vehicles that are much too large for their normal use, but they want their truck!
Very, very, very few people think rationally about vehicle ownership, and telling them, "You know, your car can go do other things while you're working," just doesn't fly. Why would I want someone else in my car? Why would I want to have to keep my car spotless for others? What if they don't for me? What if something happens and I want to go to lunch early, or there's an emergency and my car is 20 minutes away? These aren't rational concerns for most people, but even if a company managed to truly deliver level 5 automatic driving, I can't imagine the majority of people would use it to let their cars go any farther than the nearest parking spot without them.
I don't use a car near enough to justify owning one, but have considered getting one just because taxis are unaffordable for any bigger trips and carsharing can be a pain in the ass (mostly having to get to/from the carsharing station, inspecting for damages, and the lack of flexibility).
Solve those problems, and I will actively not want to own. Parking is expensive.
