High fertility and population growth have been framed as villains in global health and development. Inspired by neo-Malthusian concerns around resource depletion, scholars have argued that fertility reduction through increased contraceptive use is necessary to protect maternal health, prevent environmental disaster, and promote economic prosperity throughout the Global South. Despite substantial critique from feminist and anticolonial scholars, the scientific evidence behind these arguments has often been treated as established fact. This ostensible scientific consensus on the instrumental benefits of contraceptive use has been marshalled by the global family planning establishment in the wake of the 1994 International Conference on Population and Development to justify continued efforts to maximize contraceptive uptake in the Global South. Here, we critically examine the evidence linking high fertility to adverse maternal health, environmental, and economic outcomes, and evaluate whether reducing fertility through increased contraceptive use offers an effective strategy to address these challenges. We find the state of the evidence weaker and more conflicted than commonly acknowledged, with many claims relying on small effect sizes and/or unjustified assumptions. While increasing contraceptive uptake and reducing fertility may offer limited, marginal advantages, we argue that family planning cannot effectively address the multidimensional challenges of global poverty, ill health, and environmental degradation. Instead, global health and development should address root causes of these phenomena, while family planning programs must radically refocus on reproductive autonomy.