Tesla FSD is already being used for on a billion miles per year. Search for "Cumulative miles driven with FSD":
https://digitalassets.tesla.com/tesla-contents/image/upload/...
Usage will continue to grow as it gets better. And it got a lot better over the last months.
And then there is Waymo which proves that with geo-fencing, high resolution maps, additional sensors and remote operators on standby, robotaxis are already possible today. Tesla could add some of these too, if it wants to accelerate meeting regulatory requirements.
There is a big, hell a gigantic, difference between that and robotaxi. You need the car to be able to handle from start to finish, the entire trip, not parts of it, not even just 99% of it.
Also, the car cannot stop or be unable to deal with some situation and require help. If owners randomly have to go help their car miles away because the "taxi" got into a unknown situation, they're quickly going to get out of that deal.
And then you have all the regulatory and insurance issues. Is Tesla or the owner insuring the commercial part ? Are they required to get commercial license ? What happens if the car hit and kill someone during a robotaxi trip, who is responsable ?
Each issue Tesla can't solve in a more efficient way, they can solve by copying the competition.
2: If they want to rent cars from individual owners, they can make the conditions as comfortable as needed. Monitoring and insurance for example would most likely handled by Tesla and not be paid by the individual owner. The owner would just get a fee for every hour Tesla uses their car.