The death penalty is not a matter of personal vengeance. It is a tool society has to punish gross offenders of society's rules, and to protect its innocent.
Life imprisonment is insufficient for born criminals who can never be rehabilitated. To maintain these threats to society at public expense is a mistake.
Certainly the death penalty should not become a blanket punishment, but the people of Massachusetts can decide which crimes will be deemed heinous enough to merit this stiff punishment.