Those "nanobots" can "eat" just about anything - wrong
Main article: atomically precise disassembly
It is often thought that the capability of taking things apart atom by atom would become available just when one starts to be able to put things together atom by atom. This is far from true. Taking things apart atom by atom is a much harder problem in many cases. Beside other factors the inability to consume just about anything harshly limits the aforementioned grey goo scenario.