This society as I described it, yes, will not be very secure if there are problems that stop the miraculous post-scarcity. However, there are ways around this; firstly, provide everyone with the ability to be self-sufficient, should they so require. That means, even IF everything fails, if they've got a will to survive they'll do so. Secondly, lots and lots of backups to ensure that there's no single point of failure.
>what did you learn from the flipping of the switch? Nothing. What did you learn from a lifetime of decision making and hardship? Responsibility, autonomy, self control and a bit of common sense
The results of the flipping of the switch provides continued survival by means of eating or having a place to sleep; similarly, a lifetime of decision making and hardship produces (hopefully) continued survival of the same.
Responsibility, autonomy, self-control are all not guaranteed, and if they turn up, they're side-effects of the survival. You might as well get hate, bitterness, misantrophy (especially after working retail) and depression out of that lifetime of hardship. And you yourself note common sense is pretty rare even in working folk.
If you want to cultivate responsibility, autonomy and self control and good traits, it's better to do so directly, instead of hoping it comes about via work.
Regarding brats: One of the main reasons brats get away with being bratty is because they've got something other people want, lots of physical wealth. That allows them to get nontangible stuff like people fawning over them and so on. In a post-scarcity society, EVERYONE has got that stuff, so there's nothing to cause that behaviour. Instead, people will be trading on respect and awe, which will require some sort of ability, if they want people to like them.
As for the people who'll just connect themselves to wank machines or something? Eh, so what? They're having fun.