Edward Lanphier and colleagues marshal a familiar and, we believe, ultimately counterproductive line of argument against genetically modifying the human germline (Nature 519, 410–411; 2015, see also Nature http://doi.org/3xt; 2015).

In his essay The Rhetoric of Reaction (Belknap, 1991), the late economist Albert Hirschman describes three simplifying, stereotypical theses that are often invoked to preserve prevailing policies or practices. Lanphier et al. follow these same well-travelled tracks. They warn that a public outcry over the ethics of germline editing could hinder therapeutic applications of non-heritable genetic modification of somatic cells (the perversity thesis); that the technique might not deliver the anticipated benefits (the futility thesis); and that modifying genes in reproductive cells could be a slippery slope towards non-therapeutic genetic enhancement (the jeopardy thesis).

Such blinkered arguments can lead to sharply polarized views, obstructing the balanced and pragmatic societal discussion and careful studies that should precede possible applications of human germline modification (see D. Baltimore et al. Science 348, 36–38; 2015).