I'm not advocating for anything like that. I'm just proposing a scenario. How will people react to it? If someone decides to wage war against the world to save it, what is that? How do you judge such a person? He clearly doesn't fit into the framework of ordinary morality. He is either a villain unlike any other, or a saint.
Such situations, of course, don't happen every day, but you need to be prepared for anything.
By the way, the phrase: "It is better to destroy five billion people on Earth to save the Earth and the remaining people!" - belongs to me, but it arose in the heat of an argument at work. The argument was about consumer society.