Wait not everyone has killed someone?

It's got to be better to encourage people to be better and allow them to have a chance to change.

A good percentage of my novel (WIP, third draft) is about that. It takes place in this space age afterlife where objective and good space angels categorize and separate people by the development of their consciences. And the villains' activist group is in the self-righteous category, and they don't believe in the forgiveness and redemption of many kinds of people. The two main antagonists are a husband-and-wife duo, and the husband is bitter from tragedy after being one of the earliest fighters for womens' votes in the US on Earth. He ends up coming to terms with the harm he's now caused in the afterlife in the name of revenge against wrongdoers; and then the protagonists convince him that he too has the right to atone by being— and by doing— better.

Admittedly, since in this universe people can be reincarnated indefinitely, the harm that people cause (whether back on Earth or in this afterlife) is softened. As an interesting bonus, though, I will say that the villains did seize the means of reincarnation and start deciding who gets to be reincarnated— until the protagonists win, of course.

Also also, that theme is just like a quarter of what the novel has to offer theme-wise. It's also largely about healing from childhood trauma, mental health tools, identity discovery, found family, and kinder perspectives. Also the space angels are super cool and have interesting science-fantasy powers; and the science and sci-fi stuff is really cool as well! (Yes, I did just devolve into advertising. You would have too!)