I haven’t said that mitigating factors shouldn’t be taken into account, what I am saying is that these shouldn’t mean that someone should be let off lighter because of horrific childhoods.
But that is the essence of mitigation. These are precisely the sort of things that get taken into account by the courts every day when sentencing.
Although you claim that, when you use the word "excuse" you are referring to lightening the sentence not totally letting someone off, the rest of your post shows that you are still confusing the two.
It might help to try another example. If someone steals food from a shop for a starving child, they know it is wrong and that they may be arrested, charged and convicted, and presumably they accept that risk. Yet no-one would suggest, I hope, that they should be sentenced in precisely the same way as some idiot who comes and steals precisely the same stuff purely for fun.
In this case, Christa Pike was born with brain damage leading to learning difficulties and other problems. She lived a life where people did horrific things to her and got away with it, and when she tried to get help from people like the police she just got sent back to suffer more abuse. Yes, she probably did learn somewhere that the death penalty existed for murder.
However, what she saw all day every day was people getting away with offences without suffering any consequences, and she then came across a boyfriend who offered her some prospect of escape and became in thrall to him. She knew that she might get the death penalty for murder, but the simple fact is that that in itself does not inevitably mean that she had to. The state allowed for the death penalty to be commuted to life imprisonment if there were mitigating factors, and these factors along with matters such as her age should have been considered as such. Now, mitigating factors should also include the amount of time she has spent in solitary confinement, and the fact that she has been grievously injured by the state.
And, of course, the death penalty is wholly uncivilised and immoral anyway.