This sort of thing is horrible and the man should be punished accordingly.
Killing him would be one solution, great one less scum bag off of the face of the earth and we don't have to pay to keep him in jail.
Not exactly a moral thing I'd say, not just because killing is wrong, but because it's still not justice. How does he learn? How does he suffer pain? (Not saying we should give him physical pain, but the pain of emotion) For criminals like these, a jail as cheap as cheap can be is good, just a sturdy building, with bars, a courtyard, guards and crappy food (2 meals a day) - I say crappy food, but school food is worse than prison food (well after new studies, school food has been improved) basically running the prison cheaply as you can (I mean they don't need entertainment or leisure, just enough activity to stop them from insanity, entertainment, okay food etc. is what makes prisons too cushy)
Yes, we shouldn't pay money to keep him alive, but by keeping him alive we're delivering justice - he'd have counsellors to speak to him about what he did and they'd try and help him see the extent of what he has done. Being isolated in his cell will give him time to think, a lot of time to think and when you have that much time to think you will reflect upon what you've done and he should soon realize his mistakes. And when you see you've done something wrong your super ego kicks in and makes you feel bad about it - and the level of your actions will determine the internal pain. So when his life sentence is up, he'll know the extent of his actions. Or at least there's a good chance if he's not in a cushy prison.
Perhaps, if money and tax is an issue, perhaps our justice guys could use prisoners to work and fund themselves, (supervised and incapable of escape or harm, or enjoyment)
Plus life sentences mean you don't screw up and put innocent men to death, West Memphis 3 anyone? Alleged child murderers that has more evidence against the crime than for. (They're not dead yet, but still on Death Row)
And of course the phrase I grew up with 'Two wrongs don't make a right'. The only time I consider killing right is to prevent a greater injustice (as opposed to punish somebody for). If released he may be bigger threat to society, so don't release him (or at least until it is guaranteed that he's not a threat)...at least have a justice system that delivers justice, ours will (and has) release(d) road killers 2 years after being put in jail.
Eye for an eye doesn't equal justice.
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