Who can argue with a movement that wants to empower all of us with the best possible health, eliminating most forms of disease and promoting a massive upgrade in overall levels of intelligence and education as well as promoting happiness as an attainable and desirable immediate outcome, not something to be endlessly deferred in subservience to outmoded medieval-era slave-scripts? Quite a few people. With good reason.
Letting tiny machines loose inside people's bodies is scary stuff. For many lay-persons, the notion of nanoscale manipulation is emotionally loaded and confusing if not outright terrifying. It's uncomfortably close to manufactured plagues and germ warfare experiments, for one thing. It also crosses the line between treating illness, rectifying defects and performing enhancements or making drastic changes. Who determines what features or traits are defective or need to be replaced? Who decides what level of enhancement is enough? Remember the so called racial hygiene programs of the Twenties & Thirties that morphed into 'clinics' in the US and elsewhere? Sweden, for example, had a race hygiene program in operation until the 1970s. What sorts of things would a clinic adopting invasive nanotechnology get up to if it could operate under the aegis of a particular political party, ideology or religion? Scary stuff? You bet.
When we gain the ability to erase unwanted traits...what traits become unwanted? If we gain the ability to enhance physical ability, raise intelligence and prolong lifespan, do we do this evenly, across the board and with equality for all, or do some get it and others get the shaft? Do we get a very different sort of Haves versus HaveNots dichotomy that leads to a very messy and quite literal type of class warfare?
Will those who wish to abstain be able to remain untainted by the swarms of nanomachines let loose into the biosphere by utopia-seeking first-adopters? Will the various systems come into conflict? Is it all going to be one massive hyper-Darwinian nanoscale slugfest betwixt and between the various competing schemes? Will we get the option to be dual-booting, using more than one modality simultaneously? Or will we get colonized by the outfit with the biggest and best marketing budget?