The odds are the type of killer up for the death sentence is going to kill someone else if he's merely sentenced to prison.The killing will occur in prison and the victim will be someone in jail for a non-violent crime, or a prison guard or other person doing work there, maybe even a missionary.
The judges know this, so whether they send the killer to Old Sparky to turn him or her into a crispy critter, they've actually condemned someone else to death.
...uh...right....Mr. Dahmer will vouch for that....
When it came to Dahmer the prisoners realized that placing him in their prison violated their fundamental right to life, and to not be eaten by a cannibal.
I'm surprised Dahmer made it through the first day. Used to be the time killers like that were carved up with shanks while the guards held them down.