Will nanotechnologists accidentally or deliberately create a “gray goo” which will devour us all?

I don't think the “gray goo” scenario is credible or worth worrying about. Invincible monster replicators that eat up everything and can’t be stopped? Nonsense. What would their energy source be? We have some nasty monster replicators now in the form of viruses and bacteria. They cause some problems, but mainly we get by. See, even though they’re way more advanced than anything we will be building in the foreseeable future, they’re vulnerable to drugs. And soap. And sometimes sunlight and fresh air. Not to mention our own nanotechnological countermeasures such as antibodies.

If it were so easy to make a replicator (especially by accident!) that would eat through anything and everything, be carried by the wind, live in the wild off solar power, reproduce like crazy, be immune to poison, radiation, detergent, and everything else, and do whatever else gray goo is supposed to do, then I figure natural microorganisms would already have done it by now. From the absence of “green goo,” I infer that the creation of gray goo is, if not impossible, at least extremely difficult and not worth worrying about at this juncture.

For a nanotechnology researcher to worry about inventing gray goo is like worrying that while trying to invent gunpowder you will accidentally blow up the world.