The death penalty protects human life- it does not disvalue it. If people know that murder will be punished likewise, they will refrain from committing it. The death penalty deters violent crime, which ultimately saves innocent lives.
Additionally, the death penalty reflects society's value of innocent life. If our society values the vulnerable, we will zealously punish those who prey upon them. If we fail to execute murderers, we would be sending a message: we do not value innocent life enough to punish those who take it.