Some of the bravest and the best men of all the world, certainly in law enforcement, have made their contributions while they were undercover.
To be trained in karate is something because karate is a vicious thing. If you are any good at it, you can kill somebody with it. It is a vicious way to fight.
There are millions of kids who, naturally, if we could only remember how it is - you know, you resent authority, you are impatient for change, you want to fix things up.
There is another thing about a kid, if we all remember, that you have an attraction to evil. Evil is exciting and evil is interesting, and plenty of kids have a fascination for it.