I am of the personal opinion that the system of capital punishment in our country is failed and unjust. I believe that we need mental hospitals which provide adequate compassionate care instead of prisons; I believe that most people who do end up behind bars suffer from one form of mental illness, whether it be an Axis I disorder, mental retardation, a personality or Axis II disorder, or substance abuse.
That being said, on the issue of the death penalty, there is a legitimate machlokes. Reb Moshe paskined that it certainly has its place in our society, in Igros Moshe CM 2:68. He wrote that the Torah prescribes capital punishment for a number of grave offenses,including murder, certain types of kidnapping, adultery and idol worshiping. The transgressors in these cases, he explained, are capable of committing all kinds of atrocities and cruel acts for their own benefit. The punishment, however, was not to be inflicted because of hatred for the offender or concern for the survival of society, for it is the Jewish belief that G-d will punish the offenders (Bava Metzia 83b). The purpose of inflicting capital punishment for these offenses is to educate people about the severity of the offenses,rather than to end the life of the offenders.
On this note, R’ David De Sola Pool emphatically declared that the rabbonim approve of the theory of capital punishment, and in the post-talmudic era, it is brought down by the Rosh that mosrim were executed, and by the Rambam, as well.
On the other hand, voices like R’ Ahron Soloveichik, paskened that based on the fact that the Gemara says that a sanhedrin that executes more than 1 person in 70 years has blood on its hands, we should not support it.
I believe that the death penalty is generally the Jewish way, although in our society, based on the socioeconomic realia I mentioned above, there ought to be a moratorium for a while and then a reconsideration of how to make criminal justice work, and how to make mental health services work better for the marginalized in preventing against criminality.