I'm sorry; but, that sounds like deferrring accountability.
Not really. Just trying to find cause and effect. For an individual this is mostly guesswork but you could also research what happens with populations if the environment changes.
Besides it does not really matter. Prison is meant to correct, punish them and keep them from the street. For those that we deem not accountable mental institutions are there to cure them and keep them from the street. And some prisoners belong to mental institutions.
If you really want to make them accountable you have to go back to the old germanic system and ask her wergeld for everyone she has killed to compensate the families.
Everybody is born with limitations on what they can and can't do. How we overcome those hindrances and what we learn and achieve are what define a person. Deidre had evil parents. She had an evil being co-existing inside her body. So, her limitations were greater than any normal person experiences. But, she could have overcome these obstacles. Good people have come from bad parents. People, like Sanya and Harry, have dropped their coins. She has been in 3 books. In every book she was in, she killed people with a smile on her face and a song in her heart.
Some can and some can not, that in itself points to capabilities and lack of them. But to do so you first have to be convinced it is a worthy goal in itself. Whatever mistakes Harry makes he has a moral compass which in itself is an asset not everybody has.
To hold people as much as possible accountable for their deeds is a convention. A useful convention which helps society to function because who else would be responsible and what would people do if they discovered they were not accountable? Because holding people accountable in itself shapes environment and influences people. So continue.
But if you want to examine how people came to their actions and how free their will really was this preconception only gets in the way.
Besides accountability seems to work perfectly well without free will. When we train dogs we hold them accountable for what they do and punish and reward accordingly. Seems to work better than for a lot of humans.