The best argument for the death penalty is the one you almost never hear: we need an ultimate deterrent against criminals who already facing close to life in prison to dissuade them from rationally deciding that it's in their self-interest to kill witnesses to their crimes, such as the victims of their robberies. As Robert Stacy McCain points out in FrontPage, the latest liberal cause celebre, Tookie Williams, murdered four people in cold-blood in two separate robberies in 1979 to get rid of witnesses:
One accomplice told police: "I asked Tookie, I said, 'What you do?' He say, 'I killed him,' like that. And I say, 'Why you kill him?' He say, uh, 'So it wouldn't be no evidence.'" Williams later laughed as he bragged about the gurgling noise the dying clerk made: "You should have heard the way he sounded when I shot him."
Among his other contributions to society, Tookie is the co-founder of the Crips.