She assumed that "only the mentally handicap" could do something as deplorable as her brother so she decided if brother who assaulted me did it because he was mentally ill then mental illness is the problem and thus if we eliminate all mentally ill people then no one will suffer this way problem is her logic is fundamentally flawed people don't assault people because they're mentally ill or sick they do it because they want to and they have the power to get away with it less like scratching and itch and more like seeing a cool pen in a store that you take because you can
And thus she committed eugenics against the people who are the most vulnerable to the kind of abuse she suffered from the irony would make it funny if it wasn't both so evil and something so many people do irl
So, I think I might've read this wrong, but is she saying she's going to kill anyone with a mental illness? And the reason she killed Tang Yihes' father wasn't because he knew her plan, but because he was bipolar?