(Simplistic Observation follows)

Under 21's want to be treated as "adults." They want "what they want, when they want it." Do not understand boundaries. Believe they are "mature" enough to make decisions regarding everything. Make choices based on extremely limited experience and, frequently, extremely limited knowledge. Usually opt for "what feels good." Often are bending to "peer pressure."

(Simplistic Solution follows)

At a very young age, sometime in elementary school, we begin teaching certain "facts of life," as they pertain to crime and punishment. "You do the crime, you do the time," would be stressed. The "Scared Straight" program would be mandatory.

The program would begin with simple things like "shoplifting" and each year would be expanded to more serious crime and harsher punishment. Open discussion would be required.

If, after graduation from HS, a kid breaks a law and gets caught and convicted, he will/would have absolutely no reason/excuse for complaining about his punishment. Nor should anyone else.