"They stopped being human beings when they committed the attrocities that got them a life sentence."
No, they never stopped being human beings. No one does. Thinking that would lead you down a dangerous path - are you willing to go down hat? That some human beings are worth more than others? That some aren't humans anymore? That you treat some humans worse than cattle? Do you really want to do that? Again: serial murders objectify their victims and denied them the right of being a human being, this is what we mostly find so shocking - no mercy in their deeds, cruel, sadistic. If you pay back eye for an eye - wouldn't that make you go to the same level? I admit that some deeds want me to pay back on the same level (and when you see rape and murder of children, many feel the same) - I am human after all. I do wonder, though, if this makes me more a like to the monsters I want to kill - trying to impose the same cruelty that they did. This is maybe the question - we see how "normal" people turn to murderers, rapists and burglars during war time. Do we treat those scum as monsters and deny them being human because we don't want to be bothered with the inner monster in us all that might turn some of us in the wrong moments to monsters themself?
I am not saying that prisoners should not being made to work to some degree - I just ant to point out, you should not torture them, not humiliate them to the bone - if you do that instead of capital punishment, that would fail the point for me completely. It is nor right when prisoners are raped by other inmates, for example. That should not happen. They should serve their punishment, yes. Again - I just want to point out that you should not turn from capital punishment to Guantanamo Bay torture and applaud yourself for being humane.
"And they should NOT be allowed to profit"
Profit? Oh well ... I was never saying that. And I did not mean it at all. Being productive with doing literature, doing craftswork, doing sensible things behind prison bars can be a fulfillment on its own. I agree that - if parole is out of question - they should not receive money. If there is a possibility, or if it is not a life sentence, it even makes tremendous sense for them to save money for the life after prison. And I was not thinking about people turning their crimes into books - the media is doing that far better than them. The serial killers gave us great role models for Psycho, Silence of the Lambs, the Texas Chainsaw Massacre etc pp.
"Prisoners incarcerrated for violent crimes (murder, rape, etc.) violated someone else's rights and therefore have no rights of their own."
No, they have some rights left, not all, but some. This because they are still humans. They should be punished, but denying them the most basic human rights would defeat the purpose of a civil society for me all together. YMMV