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.

The basic parts, the start-up molecules, can be supplied in abundance and don't have to be made by some elaborate process. That immediately makes things simpler.

...Local prohibitions cannot block advances in military and commercial technology... Democratic movements for local restraint can only restrain the world's democracies, not the world as a whole.

Any powerful technology can be abused.

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.

It's a lot easier to see, at least in some cases, what the long-term limits of the possible will be, because they depend on natural law. But it's much harder to see just what path we will follow in heading toward those limits.

Nature draws no line between living and nonliving.