Very emotive subject and one hard to be truly objective about so just a few personal thoughts:
1) disciplinary actions should be corrective not punitive
2)whilst I may subscribe to the above and believe that most people should be able to be "turned around" to lead better/usefull lives despite the crimes they have committed there are blatantly instances where I would quite happily see them dead for such crimes (eg if perpetrated against my own nearest and dearest) and do the killing myself with no remorse. This is an instinctive survival thing rather than an objective intellectual view but is nontheless surely just as valid. Turn it around though and imagine that your son/daughter had inexplicably committed some heinous crime. What would your reactions be? Anger?Grief?Needing to understand "why"?Still believing that whilst deserving of punishment they should have a chance to continue living and to ultimately be able to live a better life?
3)there are perhaps many factors that may influence an individual to commit various actions including upbringing and conditioning /genetics /mental health issues. All these are factors in that individual's ability to tell the difference between "right" and "wrong" and their ability to act accordingly. At what point do we disregard these factors in judging them?
4)Despite recognizing the above I personnaly believe a few people are genuinely "evil" and cannot be rehabilitated and for serious crimes I ask why spend the time and money keeping them alive for no other reason than that if they are deemed a continuing threat to society?
5)Genetic testing/DNA/forensics. Just how reliable are they? Once they are dead you can't bring them back if there's been a mistake. Is beyond "reasonable" doubt enough?
Just some thoughts...