I didn't think that there were many people in UK prisons that were actually in for life (real life), not counting life sentences of course. Would be interested in the numbers, again not counting places like Belmarsh.
Agreed, so let's stop thinking of it as a deterrent, prison sentences aren't a deterrent for most crimes judging by the amount of re-offending.
Let's start thinking of it as punishment.
You assume a lifetime of having your actions on your conscience. What if they don't ? If you accidently killed someone you would, as would most inluding me, but I'm sure some who deliberately kill won't.