"You're 18? In that case, this lethal injection won't be cruel or unusual!"

What are they thinking??
The Supreme Court decision from yesterday regarding the death penalty for juvenile offenders is perplexing to say the least. Charles Krauthammer on Fox News yesterday had the most obvious point. (paraphrasing)

"Since only 6 nations allow for abortion on demand regardless of the term of the pregnancy, should we not ban third trimester abortions If international law is to be the standard by which we deem a law to be constitutional?"

I absolutely agree with the opinions of much smarter people than I that the SCOTUS constitutional role is not to measure national consensus, rather it is to provide judgements as to whether any given piece of legislation is consistent with the provisions of the United States Constitution. Though the language of the 8th amendment does leave a certain level of ambiguity. If the SCOTUS is required to interpret the constitution, then it is their job to determine whether a punishment legislated by congress or state legislature is "cruel and unusual". Since the founders did not deliberately define what punishments were cruel or unusual, is it not implied that this would be a changing standard based upon the acceptable conditions of any time?

My greater concern with this decision has to do with the arbitrary nature of the age of the criminal in question. In short: If it is cruel and unusual to sentence a 17 year old to death, why is it not cruel and unusual to sentence a 18-year-old, or a 20-year-old, or a 40-year-old???

Cruel and unusual is cruel and unusual. What does the age of the offender have to do with this standard? It's obvious that the path has been laid for the reversal of capital punishment for all offenders based upon the cruel and unusual standard, otherwise the "age of 18" standard for cruel and unusual is moronic.