Interesting question! I think labour camps are also problematic - on the whole, I think punitive justice in general is problematic since it's based on a fairly archaic, even animalistic, like-for-like, vengeance-oriented type thinking, and on the whole appears to be a crude deterrent that it's hard to see would endure in a truly advanced culture, where it's fully recognised that everyone - even those who commit horrific crimes without remorse - is truly a victim of circumstances that began before they were even born.
That said, I understand obviously the natural desire to exact violent retribution on those aforementioned people who commit certain viscerally horrific crimes. More importantly, it's just a fact that certain crimes are incompatible with civilised society. But the number of these crimes has been increasing since the dawn of organised judicial systems, just as the list of behaviours that are compatible with civilised society gets shorter and shorter.
Ultimately I think the desire to commit the kind of crimes that would make almost anyone question themselves about the death penalty should be and eventually will be recognised as a manifestation of serious mental illness - even if it's not one that falls easily into a DSM definition. ie, individuals who show an inclination towards deliberate, calculatedly malicious and cruel actions, regardless of whether they actually qualify as sociopathic, violently psychopathic, whatever, will be considered to be psychologically unwell - as, obviously, they are - and, if necessary, institutionalised indefinitely. Not imprisoned - institutionalised in a humane psychiatric institution.
While they are institutionalised they should be treated with kindness and compassion, no matter the scale of their crimes, and even if they give their caretakers nothing but grief.
That was a very difficult sentence to write and I can feel myself recoiling against it as I imagine the inconceivable suffering caused by certain criminals that I unfortunately know about - but I think it's the most rational approach, ultimately.
This will obviously be a very, very difficult point to get to as a species, for too many reasons to list but obviously, significantly, the aversion of a large proportion of our species to the idea of responding to horrific crimes with compassionate treatment, even if still a lifetime institutionalisation. Again, I can think of plenty of examples of crimes that would give me serious emotional difficulty with this idea, of course, as we all can, I'm sure. But, ultimately, I just don't see that our animalistic impulse to respond to violence with violence is something that can or should survive the continuing evolution of our collective human psychology beyond our brutally violent origins in the untamed natural world - and it's unavoidable that, eventually, if we are to turn our backs on the darker sides of our species, we will need to find a way to be OK with treating even the most righteously hated person with compassion.
Anything else is a half-measure that is not sustainable, and is an acceptance of a polished version of the exact dark tendencies that we are attempting to remove by exacting inhumane or even capital punishments in the first place. This, IMO, is a hypocrisy that cannot survive the continued evolution of the human race - and the human race will ultimately not survive it, if we cannot find a way to get past it.
na jk, 
).
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I'm sure that'd go down well in the consulting room!