So I pose the question: what does a person do to click that death is really, really bad?

The most common way I know is having someone close to you die. If that hasn't happened to you, try to imagine waking up one morning and learning that the person you care about the most has died unexpectedly and that you will never see them again. And if you do manage to imagine that with sufficient detail to get an emotional reaction (ie you don't flinch away from the painful thought), realize that all the other people in the world are that valuable to someone.