Must Longtermists Wish Us All Dead? A Quadrilemma

ABSTRACT Longtermists assign great moral importance to making the long‐term future as good as possible, especially by ensuring the survival of humanity. We argue, to the contrary, that on assumptions that are plausible, conservative, or shared by leading longtermists, human extinction will likely augment total utility among human and non‐human animals on Earth. The reason for this surprising conclusion is that our extinction would increase the number of sentient non‐human animals, which in turn would dramatically increase total utility. Possible responses by longtermists leave them with a difficult quadrilemma. They must either (a) welcome human extinction; or (b) welcome the extinction of most non‐human animals; or (c) tolerate continued human existence and related animal suffering as mere means to ushering in high‐tech transformations of the animal kingdom, space colonization, or digital sentience – relatively esoteric, unpopular, and speculative parts of longtermism; or (d) reject key tenets of longtermism like anti‐speciesism or the equal evaluation of making beings happy and of making happy beings. Embracing any horn of this quadrilemma would cut deep into longtermists' current commitments and/or dash central longtermists' hopes of popular appeal.