I think it is the lack of understanding of potential consequences that's really the killer. That, and young people in groups are not known to think things through before acting.

An anecdotal story from a couple of years ago. There's a field archery range that I sometimes shoot at. For the uninitiated, it's a shooting range set up in a woodland setting designed to mimic the type of shots taken while hunting. Warning signs all over the place and a fence to keep pedestrians from wandering in. I was shooting arrows at a 40 yard target when a group of teens strolled out in front of the target. Now keep in mind that there's a little over a one second delay between when the archer decides to let the string go and when the arrow slams into the target, and I was already drawing the bow for the next shot. If I been slightly faster, the lead guy would have caught the arrow.