You don;t need AI for a "gray goo" scenario. All it takes is a self-replicating nano-disassembler that is able to reconstruct extremely varied source materials into energy and copies of itself. Intelligence doesn't factor into it, any more than a natural virus or bacteria needs to be smart to eat everything it's able to eat
When I say intelligence I'm not talking like cyborgs and terminators able to make complex decisions without the ability to feel empathy. It doesn't have to be that extreme, but your point stands. You're right, all that really matters is self-replicating.
I believe it is more hysteria than anything else, but I also believe that if you don't brainstorm the possibility of unintended consequences, you foolishly run headlong in to problems.
That we can even make molecular nanotechnology in and of itself is amazing. What we know of biological replicators, like viruses and bacteria, is that they have the ability to reek havoc. Even still, they haven't consumed the world, so why would a nanobot?
Even then this placing the cart way before the horse. We don't even have true nanobots yet.
"Men never do evil so completely and cheerfully as when they do it from mistaken conviction." — Blaise Pascal
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