"A 15-year-old boy, in the hand with a shotgun he was building based on instructions he had downloaded from the Internet"
Kids aren't as mature as they used to be. Well, at least most kids aren't.
15 years old is a little young to be handling a gun (not to mention assembling a gun) unsupervised. Where were his parents? They should have been watching him.
This isnt to say I believe that kids shouldn't be exposed to guns, by their parents. Early training with firearms, and learning the 4 rules, builds a child's character and responsibility. But the parents should excersize good judgement, and supervise their children.
In this case, the parents should have been watching the kid.
I was allowed to squirrel hunt unsupervised at the age of 12. Never a gun accident.