I call these oneiric technologies: they do not and quite probably cannot exist, but they fulfil a deep-rooted dream, or a nightmare, or both. Scaling up would also borrow another trick from nature: these molecular machines would be self-replicating, being able to assemble copies of themselves. More than three decades after Nanosystems was published, Drexler’s nanotechnology is not one nanometre closer. For anyone alert to the oneiric technologies of techno-utopias and dystopias, these are red flags. We don’t have to buy the myths of oneiric technologies.