I wonder if the Superhappys could be persuaded that instead of modifying us to not feel pain at all, we could be modified to have the ability to feel pain switched off by default, but with the potential to be activated if we so chose - that would avoid their concerns about non-consensually inflicting pain on children who hadn't come to the philosophical realisation that it was worth it, but would still allow us to remain fully human if that was what we actually desired as individuals given the choice.