An analogy might help give a sense of scale here. This isn't an argument, but it hints at the scope of the unknown unknowns in nanotech space. Here on our macroscopic scale, some wonders wrought by evolution include the smasher mantis shrimp's kinetic attack, a bee hive's eusocial organization, the peregrine falcon's flight speed, and the eagle's visual system. But evolution is literally mindless -- by actually knowing how to do things, human engineering created electromagnetic railguns, networks of international trade, the SR-71 Blackbird, and the Hubble telescope. Now apply that kind of thinking to "because biology" on the nano scale...