"Of course, the embarrassment is that Justice Kennedy was overturning his own decision of 15 years before, based on "evolving standards" and laws in other countries."
First, I too question the change on capital punishment.
That said though, the Constitution state "cruel and unusual punishment", without defining what that is.
Who decides?
"who decides???"
The answer is obvious!!
The founding fathers decided, back in 1787, to allow capital punishment (its in the Constitution ... look it up.)
There are many instances of how a law has been applied ( "stare decisis") - and the idea of "precidence" means that the law should continue to be applied IN THE SAME MANNER ... unless the legislature changes the law through the process used to change the law. If the law is something embedded in our Constitution (for example - the "constitutionality of the death penalty") ... then the courts shouldn't try to change it by citing evolving standards, but the legislature is free to amend the Constituion in the manner proscribed by the Constitution.
The point is ... Judges and Justices are over-stepping the bounds of what they are legally able to do; they are now re-defining laws, so that the application of the law is different than what it used to be. That is ... plain and simple ... WRONG!!
So ... back to your question ... "cruel and unusual" can be defined by looking at how it has been applied for over 200 years. If something has been allowed for 200 years, then it becomes judicial activism when a judge suddenly decides that what was formerly acceptable and legal is now "unconstitutional" because it offends his sensibilities, or fails to comport with judicial definitions of some European country.
Mike