Idea 3: If Nano bots Get Uncontrollable, We Are Doomed

Just like everything else, the nano bots technology also comes with some frightening drawbacks. For nano bots to survive and do their job effectively in your body, they need to replicate themselves. However if they start replicating uncontrollably, all the life csn be wiped in just 3 hours - few days. This is because nano bots need carbon to survive and if they start growing uncontrollably outside the human body, they will start sucking carbon from every biomass around them whether it be from trees, humans or animals.