In 1956, a campaign by the French family planning movement (Mouvement Français pour le Planning Familial) to repeal the law of 31 July 1920 banning abortion and the sale and advertising of contraceptives sparked a fierce debate in the French media. The campaign finally achieved its goal on 28 December 1967 when the Neuwirth Act was passed, lifting the ban on contraception. The demographic argument seems to have been the one most insistently and persistently used by participants in the debate, who pointed up the potential demographic consequences of changing the law. This article examines this demographic argument, i.e. a reasoning that drew on considerations about population viewed as a geographically and historically situated collective unit. We show that it was the product of a sensitivity to population issues which was reflected in values quite widely shared in the media, notably a “pro-birth position” that reflected a preference for fertility that was sufficient to ensure population growth.