The issue here was defining "cruel and unusual" hence consulting numerous legal codes was clearly appropriate. How can one define "unusual" without determining what "usual" means?
The reference was "consider" or "consult" which is far different than "base".
Since it is the sole charge of the SCOTUS to uphold, interpret and define the Constitution of the United States, what plausible reason could there be to "consider" or "consult", as you so deftly put it, laws and/or statutes of foreign entities?
This nation and it's laws have been in existence for well over 200 years. We are the world's foremost repository of constitutional law for representative republican democracies. Additionally, we are the world's most incarcerated nation.
Given that, why would we reference these other nations for a definition of what is "cruel and unusual"?
The very fact that the Court felt the need to do this dramatically points up it's current shortcomings.
Yours is a difference without distinction.
CA....