At a moment when machines are learning to kill with increasing independence, UN Secretary-General António Guterres has drawn a moral line: artificial intelligence must not be permitted to decide who lives and who dies. Speaking with the authority of an institution built on the memory of war's worst consequences, Guterres called for a global ban on autonomous weapons systems — a recognition that some decisions are too grave to be delegated to algorithms. His warning arrives not as prophecy but as a choice point, one the international community has encountered before and must now face again.