A truck still needs to be able to drive in cities, and if you figure out how to automate all the other thing a trucker does you can replace 3 million of them. Big whoop. Robotaxis stand to challenge the economics of personal vehicle ownership, the potential market is many orders of magnitude larger.
That's plausible and incremental. No cleaning problems, no homeless people living in them, no need for remote monitoring, a far simpler liability and insurance situation, and so on.
My assumption is we'll start talking seriously about robotaxis on the day this scenario is practical and battle tested. The idea of starting with taxis seems ludicrous in comparison.
These are all solved problems, I mean when was the last time you saw a homeless person camped out in a Zip Car? BMW's ReachNow vehicles are all over Seattle and they are clean, insured, fueled/charged and exactly 0 people live in them.
I have yet to hear a compelling reason why I would give up my car, and if I did why public transit isn't a better option.