What is troublesome in the story, as you pointed out, is the seemingly arbitrary nature of God’s action in choosing whom to die, when to die, and how to die. We found someone who has such power of arbitrariness evil because in our experience, people cannot and do not have that kind of rights over another person, and so necessarily, anyone who has attempted to do so turned out evil. That is why totalitarianism is evil, slavery is evil, fascism is evil, etc.