I think Elon musk does want to "save the world", like he says he wants to, but because he's a moron he comes up with the exact kind of plan for that that you'd come up with if you tried to perfectly do the exact opposite
elon musk's plan for saving the world is basically "what if we tried fascism again, and also the Handmaid's Tale" and he has decided if you hate either of those ideas, you're an "extinctionist"