The unstated premise in your argument is that a smart person would make a robot if they had the ability. But what if a person were so smart that they could for

The unstated premise in your argument is that a smart person would make a robot if they had the ability. But what if a person were so smart that they could foresee that making the robot would be detrimental in the long term? And then you answer your own premise by pointing out the obvious reason it would be detrimental: kill-bots. We all know that is where it is headed. It is unchangeable human nature.