There is one compelling reason not to abandon the death penalty completely.  I'm referring of course to its application in situations where violent criminals already incarcerated somehow manage to torture, maim or murder other inmates or prison staff.  In cases like this, quite often the assailant is a felon sentenced to a lengthy or life term.  There simply has to be a meaningful penalty to serve as a deterrence against other inmates imitating these crimes with impunity.  Sentencing to life someone already serving a life sentence sounds absurd because, well, it is isn't it?