I will now be contrarian. I am not disgusted. I do not think it is child abuse. At least not pending further information. While some are thinking Lord of the Flies, I am actually thinking Tunnel In the Sky (albeit those kids were in the 16-21 range).
Part of this, I suppose, is that I remember reading Lord of the Flies and seeing the Star Trek episode "Miri" as a kid and thinking to myself "what a crock! My friends and I would not turn into primitive dancing cannibals if left to our own devices." As a child, I rejected it as adult propaganda. As an adult, I can say that I know some very mature children and some very adults I wouldn't want to try to build a nation with.
Part of the problem, of course, is that reality TV feels inherently exploitive, especially when you have children involved (who definitionaly cannot make the same level of informed judgment as parents). But suppose it was a university experiment? One of the tragedies of the world today -- particularly in Africa -- is the number of "child headed households" where the parents are dead and other adult relatives are either dead, cannot support the children, or will not support the children. Suppose this were an experiment to try to predict what outcomes in such societies. Would that impact the outrage level? I suspect for some, but not others.
"Reality television," when done right, can occasionally produce some educational surprises. I don't just mean the stuff on PBS like "1875 House." Sometime back, FX did a "Reality series" called Black/White, in which a black family and a white family lived together and "switched race" via make up when they went out. I recommend it.
I don't know about Kid Nation. I certainly wouldn't let my kid miss school and go away for 40 days for this, but I am unprepared to say that any parent that did is an idiot or that the premise of the show constitutes per se child abuse. I'd want to know facts first. How closely were these children watched and supervised "behind the scenes." In what environment did they live? How were their basic needs attended to? Did the participants have a right to withdraw at any time, and were they informed of that right? Were things done to artificially induce stress or conflict? Were things done to artificially increase the value of cooperative behavior? I'll wait until I see some answers before I draw conclusions. All I can say is that when I was in the 8-15 range, I would have volunteered for something like this in a heartbeat -- although I can't imagine my folks giving me permission.