I don’t know anybody who thinks a successful robotaxi service wouldn’t be a big market.
Most of the discussion has been about various aspects or arguments put forward by enthusiasts, like “it will be the end of privately owned vehicles” which seems exceptionally unlikely to me, given the convenience of owning your own vehicle and having it available 24/7 at a moment’s notice. Not that there aren’t downsides to that: purchase cost, maintenance, and for some housing it (garage, parking lot) etc. It’s just that there are multiple examples of how “renting” would be cheaper, but people still prefer to own: everything from houses to washing machines to, well, cars.
The comparison with Uber fails because there are so many differences. Uber got big quickly because they were using everybody else’s automobiles - and unused capacity - which is significant in an industry with high capital requirements. A comparison with the taxi industry is also verklempt as taxi companies had to put out big bucks to buy the metal, and on top of that buy the medallion which could run 3 times the price of the car, and then find people who wanted to “share” the daily revenue. (At the beginning the Uber split was less than the taxi-cab split. That’s not necessarily true anymore.)
The Uber model also allowed “taxi” service in areas where it was economically unfeasible to run a traditional taxicab. The car, after all, was “already paid for” and there was no medallion cost, and if someone wanted to do it in a semi-rural area they could, even part time.
All of this is to say there really wasn’t a TAM calculation that could be relied on because the services, while seemingly the same, were actually quite different under the hood.
Finally, I’ll just say that there is no proof that Tesla will be the one to walk off with the glory, or that this is a market which will provide network effects to have a single winner, so it may be split several ways. It’s also unclear if this is a business Tesla will own, or (more likely given recent statements) they will profit by 1) selling cars and 2) taking a percentage of fees. If it’s #2 (and surely that will be part of it) then there could be competitive pressure on fees, unlike taxi cab service charges which were highly regulated.
There’s still a lot of unknowns, (deadheading, cleaning, insurance, vandalism, etc.) but no, I don’t think anybody thinks “this can’t be a business.”