The fad is usually due to the whole idea of "nanobots" and "nanites" that will totally infect everything and kill cancer along the way. We can barely engineer a basic cell right now without having to severely use Mother Nature as a crutch (base DNA template, snip off as many bases as possible and see what's the least is needed to form a viable cell). A gray goo type of scenario is about as likely as AGI emerging from Minecraft and hijacking unsecured 3D printers to replicate themselves.