That’s [How about the death penalty is to show the value of human life?] such a crazy, self-defeating argument that I have nothing to add.
Who executes the executioners?
The eye for an eye principle is to ensure the punishment fits the crime. That it is neither excessive nor too lenient. How much burglary, bullion raids and stealing Botticelli's would you have to do in order to serve the same sentence as for murder? If you can work that out you can in a sense put a financial value on human life.
To use an extreme example, the 21 years plus further detention if deemed to be a danger to the public hardly seems like justice for the victims of the Norwegian murderer Breivik. It doesn't seem like justice for taking one life.
Judicial execution is not murder. If you want to take the view all killing of human life is murder except in self-defence then most soldiers who have fought in wars would count as murderers as well.
I doubt if capital punishment will actually ever be reintroduced, but that there continue to be calls for it shows some unease at the current regime in dealing with murder.