Heritable human genome editing (HHGE) to correct a nuclear gene sequence that would result in a serious genetic condition in a future child is presented as 'treatment' in various ethics and policy materials, and as morally preferable to the 'selection' practice of preimplantation genetic testing (PGT), which is subject to the disability critique. However, whether HHGE is 'treatment' for a future child, or another form of 'selection', or whether HHGE instead 'treats' prospective parents, are now central questions in the debate regarding its possible legalisation. This article argues that the idea of 'treatment' for a future child is largely a proxy for 'seriousness of purpose', intended to distinguish HHGE to avoid serious genetic conditions from less obviously justifiable uses; that HHGE is best understood, and morally justified, as a form of 'treatment' for prospective parents who strongly desire an unaffected genetically related child and who have no, or poor, options to achieve this; that HHGE would be morally permissible if consistent with that child's welfare; that legalisation is supportable with reference to the right to respect for private and family life under Article 8 of the European Convention on Human Rights; and that HHGE is morally distinguishable from PGT.