I don't think it's just public schools, I think it's a lot of things 'dumming us down'. Public school is just the most commonly blamed because it's where children spend a lot of time. I don't need a book to tell me about it - I can remember all the stupid countless hours I spent trying to entertain myself while the mercy of time did it's thing, the clock clicked, and the bell rang. If nothing else, school taught me to be patient and to make time my ally. It also gave me lots of time to mediate and think (sometimes about the ill effects of those darned buzzing fluorescents that were misaligned above our desks). For the most part, I had wonderful school colleagues and great teachers and most of them had independent studies in their classrooms, which meant you worked in a team of like-minded students, could move ahead as fast as you wanted, and socialize as much as you liked. I am really grateful for those teachers...and when I transferred schools I'm grateful that they let me enroll a year ahead and leave a year early rather than quoting some stupid law. (THey even let me finish out the year when we moved out of district! and the teachers sometimes gave me rides too.) I'm looking forward to going to my 20 year reunion this year.
Personally, I think the way the systems interact - the schools, the parents' work lives, the bus schedules, too much TV, lack of community resources, overzealous sports teams...all contribute to a type of apathy that is characterized by little thought and lots of going through the motions that are thought to be 'good', and it's this that leads to the 'dumbing down'. To do anything else requires too much effort, too much risk of social isolation, yet at the same time, very little effort (but lots of courage at the outset - a leap of faith/conviction).
Sarah