Final answer:
The person assumes that the death penalty is morally wrong, but this assumption needs to be proven.
Step-by-step explanation:
The person who argues that the state prohibits murder but then commits murder in carrying out the death penalty assumes that the justice system is self-contradictory. According to Primoratz, this person assumes that the death penalty is morally wrong. However, this assumption needs to be proven rather than assumed because there are different moral perspectives on the death penalty.