An SIS member forwarded the link https://doi.org/10.1016/j.spacepol.2022.101493 … sent to him by the author, Joel Marks, ‘The Worst Case: Planetary Defense against a Doomsday Impactor‘ and was published by the Interdisciplinary Center for Bioethics at Yale University.
Current planetary defence policy, mainly in the US, prioritises a probability assessment of risk of earth impact by an asteroid or comet in the planning of detection and mitigation strategies, and setting levels of urgency and budgeting to operationalise them. The result has been a focus on Tunguska sized space rocks capable of destroying cities and whole regions. This is the most likely sort of object we would need to defend against. However, the paper goes on to argue that a planetary defence policy on a complete risk assessment would justify expenditures much higher than at present.