So right off the bat, in the first sentence, you don't like people talking about the abuse cycle? Like just, discussing it? Because it makes you feel like they're putting the blame on someone else? You can't discuss the nuances of characters without discussing their pasts. You didn't even say people are blaming others' for their actions, you just say it feels that way. I feel like you are missing the entire point of this conversation and BSD in general.
Starting off strong with Dazai. Um. He was groomed. It's not just that he was abused. Dazai was 14, he was taken in by a man who manipulated him into the mafia when he was 14, and groomed for violence and brutality. You cannot discuss Dazai's character or his mafia days without leaving out that fact. And you say Dazai had the choice. You're right. He did. He had a choice, and he chose to leave the mafia and become a better person. It became his purpose in life, despite not having a clear view of good or evil. He left the mafia when he was 18. The entire time he was there, he was a child, and his adult life has been dedicated to helping others. He was a bad person who did terrible things, who abused Akutagawa, tortured, murdered, but you cannot separate the fact that he was groomed and a child.
I'm also going to skip to Akutagawa here and talk about Chuuya last because he's a totally different situation. Akutagawa spent his whole life on the streets, and he became violent by necessity even as an extremely young child to protect himself and his friends. Dazai took him in after everyone he knew was slaughtered, and tried to tame that part of him. Now there's nuance here in Dazai's actions as well. Dazai does respect Akutagawa and his abilities, he was attempting to teach Akutagawa self control so it wouldn't destroy him. The issue was his methods, obviously, which were overly cruel. Something Dazai himself acknowledges. Akutagawa was left with such a gaping hole by Dazai's training that he became so consumed in it, it ate him alive. Now with Kyouka, he was attempting to give her what Dazai never gave him, what he thought he needed. With both Dazai and Akutagawa's abuse, it isn't mindless cruelty because these are characters with nuances.
Just like Dazai, Akutagawa eventually tries to become better with his promise to Atsushi. He's still in a dark place and a bad situation, absolutely, but he is recovering, he is making efforts to be better. He was a kid who grew up in violence, had that part of him nurtured, and still made the conscious effort to make a change. He just had a whole arc of coming to peace with himself and Dazai. You absolutely cannot separate these characters from their past. And what's the point of trying to?
On top of that, why would you not mention Oda? Or Fukuzawa, Kyouka, etc?
Oda was an assassin from a very young age for money, to get by as a child. He felt no emotion for who he killed, he didn't care who the victim was, and he "didn't even mind killing". He was desensitized to it very young. Just like Dazai, just like Akutagawa. And just like Dazai, he made the choice to leave it behind. He did everything he could to move on and make a better life for himself until he was pushed to his limit and snapped.
Fukuzawa started killing as an adult, and he didn't just "not mind it", he enjoyed it. He liked the thrill. That's what scared him, and he too left it behind by choice and made the change to become a better person. He was wracked with guilt and despair over his past, sure, but he still enjoyed killing.
Kyouka was just as young and Dazai and Akutagawa. She was taken in and used as a tool for killing. She struggles with seeing right and wrong like Dazai was, and she left that world like Dazai did. What is your view of "forced" here? I assume you think she was more forced than Dazai was, and to an extent, I'd agree, but you are removing the psychological aspect of manipulation. Kids are affected by these things. Sometimes, they turn out badly because of it.
It's not about justifying their actions or blaming someone else. You can recognize someones actions as bad and still understand where they came from and how they ended up like that, and see that it does not make them, to their core, a bad person. BSD has such heavy themes of recovery, through Atsushi, Dazai, Yosano, Oda, Akutagawa, etc, etc. To ignore their past and their efforts to change you're missing such a fundamental piece of what makes BSD. There is nuance in every single character that you're just missing by writing them off to be evil.
Now, as for Chuuya. He's more of a tragic character in this realm. Chuuya had no out. He had no choice but to join the mafia or risk them killing the Sheep. The one time he was offered a chance at a better life, to live in the light, Verlaine murdered it. Chuuya wanted to leave the mafia. He wanted Murase's help. But Verlaine killed him, and Chuuya was driven deeper into the mafia. Dazai was given help to leave. He had Ango to wipe his record, Tanaeda to find him a job, and the agency to give him space to grow. Chuuya does not have that. He has no support outside the mafia. I'm not saying this makes him a good person, I'm saying it makes him a tragic character.