If you mean the mental/emotional state necessary for a human to act without regard for consequences of their actions to other people, then computers are not ruthless.
If you just mean acting without consideration of how their their actions will affect people then computers fit this definition of ruthless perfectly by virtue of not being able to consider the consequences of their actions on other people, because we don’t know how to program them to consider how their actions will affect other people.
I don't understand, what am I missing?
I've never seen a computer have any regard for the consequences of its decisions. Computers are thus completely ruthless.
edit: typo
We don't have to. For example, a ruthless train door could be made less ruthless, by having sensors that respond to someone who is nanoseconds late, to open the door, just that once, just like it's elevator door brethren, but only once.
The problem is that "inherently opportunistic people" will take advantage of the machine kindness and take an entire train full of people hostage.
The oppressive train door is a dictator everyone loves, maybe if they were also razor sharp, people would give them the respect they deserve. phwump. guillotrains. on time, every time.
There's also unexplored (by article) concept of inadvertent or emergent control.
E.g. Dept A encodes Rule 1 and Dept B independently encodes Rule 2, yet applied together Rule 1 and 2 produce an unexpected outcome. In which case, neither Dept A or Dept B (the ostensible controllers) could be said to actually control the outcome.