We review a class of adverse environmental externalities that accompany consumption and procreation. We also identify externalities that are traceable to socially embedded preferences for family size. Those preference structures can give rise to a heightened demand for children, exacerbating the environmental externalities households impose on future generations. Our analysis exposes weaknesses in basing family planning programmes entirely on individuals' reproductive rights. We use ecological data to obtain a feel for the size of global environmental externalities. We estimate the size of world population the biosphere can support at the standard of living enjoyed in the World Bank's list of high middle-income countries. Today's global population and future population projections far exceed our estimate, implying that the UN's Sustainable Development Goals are in all likelihood unsustainable. We conclude that family planning has been undervalued greatly by national governments and international agencies. Our purpose is to pose questions that continue to be neglected in the development literature. We do not offer forecasts nor make policy recommendations.