There are human beings whose psychological capacities are rivalled or exceeded by many non-human animals; such humans are often referred to as 'marginal cases'. R G Frey has argued that there is no secure, non-arbitrary way of morally distinguishing between marginal humans and non-human animals. Hence, if the benefits of vivisection justify such painful and lethal procedures being performed on animals, so is the vivisection of marginal humans justified. This is a conclusion Frey is driven to with 'great reluctance', but (...) which he can see no way to avoid. This paper points out a feature of the condition of marginal humans unnoticed by Frey and his critics: such humans have suffered a tragic harm. It points towards an analysis of this harm, in terms of counterfactuals holding for marginal humans but not for psychologically equivalent animals. Finally, it discusses the moral implications of the harm that such humans have suffered, and argues that it serves as the basis of a defence for preferring humans to non-humans in cases of morally inescapable conflict. (shrink)