Gyngell and colleagues consider that the recent Nuffield Council report does not go far enough: heritable genome editing is not just justifiable in a few rare cases; instead, there is a moral imperative to undertake it. We agree that there is a moral argument for this, but in the real world it is mitigated by the fact that it is not usually possible to ensure a better life. We suggest that a moral imperative for HGE can currently only be concluded (...) if one first buys into an overly deterministic view of a genome sequence, and the role of variation within in it, in the aetiology of the disease: most diseases cannot simply be attributed to specific genetic variants that we could edit away. Multiple, poorly understood genetic and environmental factors interact to influence the expression of diseases with a genetic component, even well understood ‘monogenic’ disorders. Population-level genome analyses are now demonstrating that many genetic ’mutations' are much less predictive than previously thought 1. Furthermore, HGE might introduce new risks just as it reduces old ones; or remove protections not yet clearly delineated. (shrink)