Precise editing of the human germline has been considered an unlikely and an unethical proposition. Recently, tools to edit the human germline have been developed and it is now a realistic prospect. Consequently, the ethical arguments around prohibiting human genome editing need to be re-evaluated. It is anticipatable that using it to eradicate disease-causing mutations will be acceptable if clinical risks can be shown to be sufficiently low. Some go further and advocate that genetically 'enhancing' humans will also be permissible. Here I argue that there are instances where human germline editing should be prohibited because harms can be anticipated from the results of studies of aspects of human psychology. The example I have chosen to illustrate this argument is prolongation of the human lifespan. Cohort and longitudinal studies demonstrate that a vital ingredient of human contentment and health is being integrated into a cohort of similarly aged people and experiencing life's trials and tribulations contemporaneously. A person genetically engineered to live longer than their peers will experience the loss of their cohort and many from the generation following them-an established risk factor for discontentment and ill health. Since germline genome editing precludes obtaining the consent of the individual in question, and that such a predictable harm will be commonly encountered, it is questionable that human germline editing to extend lifespan can ever be considered an ethical practice.