Any powerful technology can be abused.

If you take all the factories in the world today, they could make all the parts necessary to build more factories like themselves. So, in a sense, we have a self-replicating industrial system today, but it would take a tremendous effort to copy what we already have.

And that because the moving parts are a million times smaller than the ones we're familiar with, they move a million times faster, just as a smaller tuning fork produces a higher pitch than a large one.

Plants with leaves no more efficient than today's solar cells could out-compete real plants, crowding the biosphere with an inedible foliage. Tough omnivorous bacteria could out-compete real bacteria: They could spread like blowing pollen, replicate swiftly, and reduce the biosphere to dust in a matter of days. Dangerous replicators could easily be too tough, small, and rapidly spreading to stop - at least if we make no preparation. We have trouble enough controlling viruses and fruit flies.

In a sense, artificial intelligence will be the ultimate tool because it will help us build all possible tools.

On the molecular scale, you find it's reasonable to have a machine that does a million steps per second, a mechanical system that works at computer speeds.

I've encountered a lot of people who sound like critics but very few who have substantive criticisms. There is a lot of skepticism, but it seems to be more a matter of inertia than it is of people having some real reason for thinking something else.