The eugenicists’ espousal of the rights of the child was rhetorical. Invoking an unborn child’s rights – to anything but being born, that is – was a one-liner that allowed Gamble, Popenoe, Butler, and others to reframe their argument in favor of sterilization. This reframing based on rights, however, ultimately challenged and constrained eugenicist projects. It challenged them because conceding that an unborn baby has rights rests, at best, uneasily with abortion: the same premise is, of course, a foundation of the anti-choice/pro-life position. It constrained them because it suffered from an age-old problem affecting eugenic sterilization in North America: it would only ever encompass a small number of people. With the exception of North Carolina, only people in institutions were targets for sterilization in North America, and those in institutions were only a fraction of the targeted population of feebleminded – a fact supporters of eugenic sterilization frequently bemoaned. If the pro-sterilization movement were to survive the onslaught of Hitlerian science and increase its impact, it needed another ideological basis.

World population growth supplied part of the new basis. In the pre-First World War period, a wide range of thinkers sympathetic to eugenics were chiefly motivated by population decline, above all among the genetically fit. Indeed, the differential birthrate between the upper and lower classes was an anchor of the argument that eugenic sterilization was needed to ward off race suicide. As historian Richard A. Soloway comments on the British case, “one of the most compelling factors in the rise of eugenic analyses was the declining birthrate in general and its class differential characteristics in particular.” During the interwar period, a number of eugenicists switched horses dramatically: population growth, not population decline, was the greatest threat to racial health. This emphasis intensified after 1945, with the conventional concern about class differentials in birth rates (too many poor, not enough births in the educated classes) becoming an implicit rather than explicit focus.