Ingmar Persson challenges1 an argument in my book Humanity's End: Why We Should Reject Radical Enhancement2 that harms predictably suffered by unenhanced humans justify banning radical enhancement. Here I understand radical enhancement as producing beings with mental and physical capacities that greatly exceed those of the most capable current human. I called these results of radical enhancement posthumans, though I think that Persson may be right that this is not the most felicitous name for them.

The focus of my argument was the possible improvement of moral standing brought by the radical enhancement of human cognitive and affective capacities. This would give stronger moral entitlements to benefits and stronger moral protections against harms. My opposition to varieties of enhancement that have this effect is grounded in significant harms for unenhanced humans that predictably result from a loss in relative moral standing. Significant benefits for the radically enhanced won't morally compensate for the victimisation of the unenhanced worst off.

Persson criticises a more moderate presentation of my conclusion than the one that I favour. He presents me as arguing that …