Understanding his mental state is important but it does not excuse the actions that he took. He crossed the proverbial line many times over at the detriment of others. His intentions may not have been filled with malice but his actions were undoubtedly evil. Maybe in hell he'll understand the weight of his actions.

The demons in demon slayer get more of a pass than Traumerie because they were essentially manipulated to eat humans. Traumerie deserves to be dragged into hell by all the souls that he experimented on. He doesn't deserve any last minute touching scenes because he was rotten for most of his life.

I don't think siu tries making people sympathize with his characters more just show why they did the things they did like white or in this case the guy who killed himself have been alive for so long and has become so disconnected from reality that he can't see them as people anymore and in the past chp all the family heads had to make hard choices which involved killing people these repeated actions took away their humanity hence why he did those things cause he lost his humanity