Justice Breyer argues that the Death Penalty is Unconstutitional

In his dissent in Glossip v. Gross, Justice Stephen Breyer argued that the death penalty violates the Constitution's ban on cruel and unusual punishment. Some excerpts:

In 1976, the Court thought that the constitutional in­firmities in the death penalty could be healed; the Court in effect delegated significant responsibility to the States to develop procedures that would protect against those con­stitutional problems. Almost 40 years of studies, surveys, and experience strongly indicate, however, that this effort has failed. 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.

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Researchers have found convincing evidence that, in the past three decades, innocent people have been executed. . . . The evidence that the death penalty has been wrongly imposed (whether or not it was carried out), is striking. As of 2002, this Court used the word "disturb­ing" to describe the number of instances in which individ­uals had been sentenced to death but later exonerated. At that time, there was evidence of approximately 60 exonerations in capital cases….Since 2002, the number of exonerations in capital cases has risen to 115…Last year, in 2014, six death row inmates were exonerated based on actual innocence. All had been imprisoned for more than 30 years (and one for almost 40 years) at the time of their exonerations. . . . Researchers estimate that about 4% of those sentenced to death are actually innocent.

Because of the high rate of errors in capital trials, Breyer argues, the system must provide for very extensive reviews, which regularly take decades, which largely undermines the deterrent effect (if any) of the death penalty:

And that fact creates a dilemma: A death penalty sys­tem that seeks procedural fairness and reliability brings with it delays that severely aggravate the cruelty of capi­tal punishment and significantly undermine the rationale for imposing a sentence of death in the first place...(one of the primary causes of the delay is the States’ “failure to apply constitutionally sufficient procedures at the time of initial [conviction or] sentenc­ing"). But a death penalty system that minimizes delays would undermine the legal system’s efforts to secure relia­bility and procedural fairness.

In this world, or at least in this Nation, we can have a death penalty that at least arguably serves legitimate penological purposes or we can have a procedural system that at least arguably seeks reliability and fairness in the death penalty’s application. We cannot have both. And that simple fact, demonstrated convincingly over the past 40 years, strongly supports the claim that the death pen­alty violates the Eighth Amendment.

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[T]he crimes at issue in capital cases are typically horren­dous murders, and thus accompanied by intense community pressure on police, prosecutors, and jurors to secure a conviction. This pressure creates a greater likelihood of convicting the wrong person.

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Thus, whether one looks at research indicating that irrelevant or improper factors—such as race, gender, local geography, and resources—do significantly determine who receives the death penalty, or whether one looks at re­search indicating that proper factors—such as "egregious­ness"—do not determine who receives the death penalty, the legal conclusion must be the same: The research strongly suggests that the death penalty is imposed arbitrarily. . . .

The studies bear out my own view, reached after consid­ering thousands of death penalty cases and last-minute petitions over the course of more than 20 years. I see discrepancies for which I can find no rational explanations... Why does one defendant who committed a single-victim murder receive the death pen­alty (due to aggravators of a prior felony conviction and an after-the-fact robbery), while another defendant does not, despite having kidnapped, raped, and murdered a young mother while leaving her infant baby to die at the scene of the crime...Why does one defendant who committed a single-victim murder receive the death penalty (due to aggravators of a prior felony conviction and acting recklessly with a gun), while another defendant does not, despite having committed a "triple murder" by killing a young man and his pregnant wife?... For that matter, why does one defendant who participated in a single-victim murder-for-hire scheme (plus an after-the­ fact robbery) receive the death penalty, while another defendant does not, despite having stabbed his wife 60 times and killed his 6-year-old daughter and 3-year-old son while they slept?... In each instance, the sentences compared were imposed in the same State at about the same time. . . .

The imposition and implementation of the death penalty seems capricious, random, indeed, arbitrary. From a defendant’s perspective, to receive that sentence, and certainly to find it implemented, is the equivalent of being struck by lightning. How then can we reconcile the death penalty with the demands of a Constitution that first and foremost insists upon a rule of law?