Even if a civil society were to be dissolved by the consent of all its members (e.g., if a people inhabiting an island decided to separate and disperse throughout the world), the last murderer remaining in prison would first have to be executed, so that each has done to him what his deeds deserve and blood guilt does not cling to the people for not having insisted upon this punishment; for otherwise the people can be regarded as collaborators in his public violation of justice.
It isn't the desire to abide by the law that makes everyone behave as society requires, but the fear of punishment. Each one of us carries a gallows inside us.
Exploration was for those with a measure of peasant blood, those with big thighs and thick ankles who could take punishment as they took bread and salt, on every inch of flesh and spirit.
I personally have always voted for the death penalty because I believe that people who go out prepared to take the lives of other people forfeit their own right to live. I believe that that death penalty should be used only very rarely, but I believe that no-one should go out certain that no matter how cruel, how vicious, how hideous their murder, they themselves will not suffer the death penalty.