There are a lot of people who behave like they are still in high-school...
Since evidence suggests that "cliques" and "bullying" continues through university and into business** being exposed to it and learning to deal with it is likely an important life skill to be learned (similar to EQ, and perhaps arguably more important than academics). I'm not saying home schoolers (of which I know a few) can't learn these skills, but depending on your career aspirations, growing up in "tougher" environments can often be a formative learning experience for young folks.
They are more professional, less crass and boorish.
You say that like it's good to be professional all the time and bad to ever be crass and boorish. I guess to each his own, but personally, I would find a such a permanent professional veneer existence rather sterile and boring (even in the office)...
They don't attract notice except in passing to note someone seems strangely confident in themselves.
FWIW, confidence is a two edged sword. The risk with confidence, is over-confidence, and not knowing yourself. This in itself can benign in the form a comparative-optimism which can contribute to delusion that they are more likely (than average) to have good things happen to them and less likely (than average) to have bad things happen to them which often leads to a happier life. Or in the other extreme a Dunning-Kruger handicap throughout life. More confidence is not always better, but more self awareness generally doesn't hurt (too much, although can be depressing at times).
Sometimes it's hard to find out who you are and develop self-awareness when constantly in an environment created by your parents. I've seen that happen many times in my university (with both home schooled and highly sheltered children), since they weren't exposed to a more free-wheeling environment before, they we just discovering who they were when the consequences were much higher (if you want an analogy, not unlike getting the chicken pox early in life vs when you are an adult, or learning to drive for the first time on your playstation vs with a 1/2 ton steel box with seatbelts and airbags).
There is also some evidence that artificial confidence can be crippling for some children (e.g., forced to show artificial confidence, but knowing they are untested, some children are extra fragile when confronted with failure and develop coping strategies than can be self-defeating or even anti-social).
**They range from the more benign "lunch-invite-crowd", cafeteria table, smoke-break crew, to the more malignant country club good-old-boy variety and everything in between. Some folks just call this office politics to make it somehow sound more mature, but it's really just the same thing...
