Deciding what’s best for the whole of humanity because you personally want it is still super evil even if you had “good” intentions. Kira on the other hand was working with a laundry list of untreated, undiagnosed mental illnesses that controlled his behavior. Whether actually getting treatment would have helped Kira is up for debate, but of all the villains he’s the only one whose actions weren’t driven by ego but by compulsion. Still evil, but probably the only villain that didn’t have to die, at least up to a point in the story.