Pamela Karlan shines a light on how it disrupts the rest of the legal system:
[Douglas Berman of Ohio State] has calculated that about one in ten thousand state felony sentences is a death sentence, yet the Court devotes more resources to reviewing death sentences than to reviewing claims in all other criminal cases combined. And while the Court has repeatedly considered whether a death sentence is proportionate to a particular class of crimes—for example, barring death sentences for non-homicide offenses or for juvenile or mentally retarded defendants—it has set virtually no limits on the severity of prison sentences. In the 40 years that the Court has been actively policing capital punishment, prison sentences have lengthened and the U.S. prison population has skyrocketed. With execution at the top end of the scale of punishment, a life sentence begins to look something like leniency, and other sentences are inflated in turn.
The Dish 