I wouldn't necessarily say that it's for people who don't know how to drive, or that they're bad/scared driver. I definitely agree with the screaming part though.
For the sake of argument lets say FSD worked really well, but due to regulatory issues it still has to be supervised.
Who does it benefit in this case?
I think it comes down to special use cases.
Whether they admit or not a lot of drivers are intimidated by stop sign controlled intersections that have a lot of cars arriving at the same time, and people going all sorts of directions. It's just too many cars for the human brain to keep track of. Heck half the time that I arrive I don't even know when the other cars to one side of me arrived as my vision is blocked by a car in the lane next to mine. I'd love for FSD to work as well as could be expected here.
The other case is areas where the driver isn't familiar with. There are a lot of intersections that aren't well thought out, and its not always clear about what lane goes where. It would be nice if FSD had pre-mapped knowledge of the intersection, and knew exactly how to handle it.
There are also other cases where I simply don't have the patience for an intersection. Like I tend to avoid unprotected lefts across multilanes of traffic because there is too much traffic. So I simply take a right and I go around. The total time is probably about equal.
I'm not particularly keen on roundabouts either. I enjoy the singe lane ones, but beyond that I start to get nervous quick.
Where I hope to use an FSD component the most is parking. I wish I could just exit my car and have the car go park itself. I'm the kind that will park blocks from where I want to go just so I don't have to deal with people/parking.
Even Tesla had a good reverse summon I might even go to Costco.
Obviously once they get to automated driving the use cases go up considerably. I'd love to have an autonomous camper van that would autonomous drive to the next camping spot as I hiked/biked down the coast. Now I know other people get these things called spouses and/or they pop out a kid. But, can't a robot do this? I don't really have much to say and spouses generally want someone to talk to.