Well, we've recently just had a situation where a self-replicating machine killed a lot of us, so it isn't completely insane. That said, I don't really spend much time worrying about people deliberately creating killer viruses and less worrying about more exotic artificial machines.

The protein folding idea he originally proposed seems a lot more plausible now, but yes, it was all just speculation back then. AI suddenly seeming to escape from it's long relegation to sci-fi back to reality did make me wonder whether nanotech will have it's day again though.

All that was a generation ago now. I remember reading Engines of Creation, Unbounding the Future and the fiction book The Diamond Age. Then molecular nanotech went out of fashion.

His original idea was to engineer proteins to fold up into the machines we want, and of course the protein folding problem is largely solved now, so maybe the whole idea will have its time again.