Or just catch a flight that's 1.5s hours for something that's safer than driving? Even if FSD is safer, there are many bad drivers on the road as we probably all can agree on. I checked Southwest and there are flights as cheap as $46/1 way. You still need to charge on the way there as well as charge after arriving which isn't free (and expensive in CA).
Having a car at your destination is nice, especially if it's your own car with all your stuff, but I am not sure I agree with you that there will be many takers at $300/trip, add in all the charging/time/higher risk driving vs. a flight, even for a small family.
Honestly, I'd probably balk at $300 too... but with my personal location relative to airports, I'd probably be debating driving manually versus paying for a hypothetical temporary FSD overnight pass.
There's lots of gray areas and uncertainties, and everybody does different calculations. Many people are much more fearful of flying than driving, even though statistically flying is safer per passenger-mile. Admittedly, even if the data shows that a future, true FSD car is 10x safer than driving manually, there will still be many people afraid to let the computer take the wheel.
And of course, many people still have to drive a considerable distance just to get to an airport, so flying still requires a lot more time than the flight itself, and still includes a good deal if that driving risk anyway.
Not sure if you read my rambling "spoiler," but there can be a lot more time associated with flying than just the flight itself. If you live a reasonable distance from the airport, and your true destination on the other end also isn't super close to the destination airport, then when you add up all the ground transportation and airport logistics, and what always feels like a lot of time waiting for the plane to board...waiting for departure from the gate...taxi...take off...fly...land....taxi again...deplane...more airport logistics....it adds up. For many folks, taking a short flight still means that it took them 5-6 hours or more from when they left home to when they actually arrived at the place they were trying to get to, and it all had to happen on the airline's schedule. In that case, a 7 hour drive doesn't look so bad, especially if you've got kids to wrangle. And that driving option gets even better if there's a magical future car that you can use daily, but that a family can also sleep in while the car just drives itself overnight.
Again...just crazy far future hypotheticals. But I'd love the option of just hopping in the car after dinner, watching a movie with the family, then going to sleep and waking up far far away. If trains were more plentiful in the US with stations all over the place, that would also be a good alternative...but I think the nearest train station for me is even farther than the nearest airport, and the train probably has even fewer departure time options and takes longer than driving for most routes.