I would rank nanotech as fairly low on my list of concerns, because cells are fairly close to optimal replicators in the present environment. (IE, I don’t buy the grey-goo stories: the worst that I find plausible is a nanobot plague, and normal biological weapons would be easier to make.)
I’m not sure whether this response is “within the spirit of the question”—but the primary actual problem with nanotechnology—if it is somehow magically delivered into our hands without superintelligence—is that it then massively facilitates the construction of intelligent machines and robots—by providing a high speed, low cost, efficient computing substrate—along with sensors and actuators for it to use.
I’m not sure whether this response is “within the spirit of the question”—but the primary actual problem with nanotechnology—if it is somehow magically delivered into our hands without superintelligence—is that it then massively facilitates the construction of intelligent machines and robots—by providing a high speed, low cost, efficient computing substrate—along with sensors and actuators for it to use.