To me, the rite of passage is a signal that a child is grown up regardless of age. High school graduation is one such ritual that squarely puts a young adult at a crossroads with choices to be made. Hopefully, the young adult has been given the tools to make wise decisions in situations in which he/she may be held accountable.
Having said that, however, a young adult who graduates under the age of 18 is still legally under parental supervision regardless of where they live and what they do. The law still considers the young adult a minor so that needs to be figured into any equation especially in situations where the law may be broken despite the "maturity" of the participants.
Quite frankly, having to "experience everything once before the age of 18 in order to cope with the rest of my life theory" makes no sense. I don't blindfold my child, shut him in a room with PG rated films and books til he's 18 and then release him into a world with no boundaries. Each experience is a building block designed to help him make prudent decisions as he begins his adult life. My building blocks may be different than others'; however, I feel that mine test the boundaries of freedom in such a way as to help my underage child understand how to make choices when I'm not around to make them for him.
I find it interesting that you brought up the legal aspects of parents of under 18 year olds being responsible for their actions since the vast majority of the nay-saying on this thread has not been related to the possibility that the kids may engage in something illegal while travelling (drinking, drugs) but rather the concern has been over sex and "playing house" neither of which would be illegal.
