Justice Breyer perfectly captured the major problem with the death penalty
From his dissent:
Today's administration of the death penalty involves three fundamental constitutional defects: (1) serious unreliability, (2) arbitrariness in application, and 3) unconscionably long delays that undermine the death penalty's penological purpose. Perhaps as a result, (4) most places within the United States have abandoned its use.
I shall describe each of these considerations, emphasizing changes that have occurred during the past four decades. For it is these changes, taken together with my own 20 years of experience on this Court, that lead me to believe that the death penalty, in and of itself, now likely constitutes a legally prohibited 'cruel and unusual punishment.'
Three Oklahoma inmates brought the case and had argued that the drug midazolam violated the Constitution's bar on cruel and unusual punishment. However, the court's conservative justices ruled on Monday that the inmates failed to show they'd be able to prove those claims.
"[T]he prisoners failed to identify a known and available alternative method of execution that entails a lesser risk of pain, a requirement of all Eighth Amendment method-of-execution claims," Justice Samuel Alito wrote in his majority opinion.