First, I think they would question this notion of the victim getting justice. The murderer dying obviously does not help their primary victim get justice. And then does it give the family justice if the murderer is killed? It depends on what one thinks is just. Nothing is bringing back the dead person, which would really be the only true justice. I think giving people the impression that someone else's death is giving them something they need is misleading and harmful. They are still going to feel like shit. There is a difference also between a hot killing and a cold killing. If I come home and find someone has killed a family member and they are standing there with the weapon, I may kill them, if I manage. Good chance I think. But once you have someone in custody and have control of the situation, it is a whole other thing to coldly go about setting up their death. And this process damages society, many anti-capital punishment people will argue. You may not agree, but notice that their concern is not simply for the murderer.Not necessarily in this case, but in many others anti-capital punishment people almost seem to be defending the criminals, yet they don't bother with the victim getting their justice.
I think the process of relating to a person for months or years, then escorting them to a cold death is damaging. For all the various people who engage in that escorting, and even to we who are at a distance. It affects what we are. You may not agree, but that is part of my position. I can't be sure it is part of Enmos'.
Then there are a range of practical issues. It is a horrible, horrible thing for a country if they put an innocent person to death. Of course it is horrible for that person, but it damages the spirit of a country and all the people who put that person to death when that happens. And it does happen. And sometimes we do find out.
Another problem, in the US, is that if you are black you have a greater chance of being killed by the state than if you are white. Guilty or innocent. Until that is fixed, the spirit of the country is damaged by the death penalty.
There are other issues, but those are a start.
And remember these guys are in prison. It is not as if people are advocating no punishment.