Here:

Perhaps even more important, he concluded that "the character of a juvenile is not as well formed as that of an adult." For all these reasons, wrote Kennedy "the penological justifications for the death penalty apply to [juveniles] with lesser force than to adults." The twin social goals—of retribution and deterrence—are not served if the offender is not as culpable as an adult for their crimes.

Has Kennedy heard of overdetermination? If you nuke NYC and I nuke the entire state of California, we both deserve the ultimate penalty, death, but you are less culpable. So, differences in culpability don't always imply differences in suitable punishment. Similarly, if you were stupider or more prone to reckless behavior than some adult murderer, it doesn't follow from that that you weren't sufficiently culpable to warrant the death penalty ... it may only mean the adult was much more culpable.

How is two young men attacking, robbing and raping a 72 year old woman were taking a "youthful "risk". It was a calculated selection of a victim who could not fight back and not an impulse.

Even as we speak, there is a news story of a paroled sex offender who raped and murdered 10 women. There is another sex offender in California who kept 1 child prisoner and suspected for the two other murders of preteen girls.

How many times do we have to hear about innocent lives damaged or lost in the henious attacks. As for cruel and unusual, use the criminals own crime as the yardstick. By comparison anything the government does will be kindness itself.