  The distinction between therapy and enhancement, as it applies to both somatic cell and germ-line GM, is also considered by some bioethicists to have moral significance: interventions that restore normal function from a state of disease or disability (negative GM) are considered permissible whereas interventions that improve on normal function (positive GM) are  not.[57] Arguments against genetic enhancement include: clinical risks outweigh possible benefits (Anderson 1990); it violates parents’ fiduciary responsibilities (Schonfeld 2003); genetic diversity will be diminished (Parens 1995); the socially acceptable range of traits will be narrowed (Agar 1995); the principle of equality of opportunity (Daniels 1994) and the Rawlsian imperative to help the worst off (Fleck 1994) support negative but not positive GM; appreciation of shared human “fragility” and the accomplishments of individuals may diminish (Parens 1995). A further distinction can be drawn between enhancements that go beyond species typicality to improve health (e.g. disease-resistant genes) and enhancements of social value (e.g. eye color), and it is argued that there is no moral difference between using GM to augment function and using GM to restore function if the aim is disease prevention (Harris 1993; Juengst 1997). Some bioethicists who support GM for enhancement as well as therapeutic purposes counter these arguments by asserting the reproductive autonomy of parents (Stock 2003). Others point to the lack of an objective and/or morally justified distinction between therapy and enhancement, health and disease (Goering 2000; Resnik  2000).[58] Indeed, with GM, we humans ourselves determine what counts as “normal” genetic variation, no longer needing to look to a pre-existing species-typical functional norm (Resnik 1997b). The moral permissibility of particular genetic interventions, therapies and enhancements alike, might instead be assessed according to Rawlsian principles—with equality of opportunity and concern for the worst off supporting the prohibition of some enhancements and the guarantee of a minimal level of genetic health (Resnik 1997b), or a permissible intervention one which, when contemplated in the original position behind a veil of ignorance, can be seen to prevent a condition that would be detrimental in all societies or bring about a condition that would never be detrimental in any society (Goering 2000).