While I agree in general the idea is that Machines do far less and have far less variables because it's usually a specific task, and they aren't susceptible to the problems that humans are i.e. fatigue food hunger etc. those things generally can be better controlled the regular maintenance schedule than human. It's rare for a properly taken care of for machine to randomly get sick in the middle of it's shift where is for human we all know you get sick at any moment. So to speak.
Many human illnesses come from not being properly maintained. In a perfect world the mechanized helpers would be perfectly maintained and never break down. But people, the flaw in the process as Stewart points out, are involved in making sure their devices are perfectly maintained. Just as the human body is only as good as the way each individual treats it devices are only as good as their maintenance schedule.
There seems to be a disconnect ... the thought that humans are so flawed that we need to replace them with machines. Yet somehow the machines will be less flawed than their creator? When a flaw is pointed out in a machine the answer is "we can fix that" yet when flaws are pointed out in humans the attitude is "give up we're beyond hope".
The problems that face the human machine are solvable. Fatigue can be cured by rest. If eight hours is too long to go without refueling how about having a lunch? Make the lunch an hour so the body can be properly refueled. If four hours is too monotonous to work then schedule a break. If the manual for our devices says to shut down reboot the system every hour and refuel every four hours why is that accepted as "normal maintenance" for a machine yet "goofing off" for the human machine?
More serious faults can develop in machines as well as humans. I've worked at places where machines "randomly" got sick. Yes, often the random illness can be traced back to the user (please don't execute attachments!). But now we're back to the "flawed humans" who will, as Stewart suggests, remain part of the process no matter how mechanized one tries to make the world.