Once someone would taste that power, they’d undoubtedly kill anyone that in their mind is evil, but may have lead to the best outcome.
Power corrupts.
Absolute power corrupts absolutely.
I doubt these assertions, because almost everyone has power; almost everyone can kill, steal, rape, and many other immoral actions if they wished to do so, but don’t because of their acknowledgement of authority, although the opposite occurs when authorities demand such acts. The external authority held over subordinates is upheld if the subordinates don’t pay mind to the mortality of their external authorities. However, in the case of internal authorities, self-preserving and procreant instincts and empathy, these hold the most sway over one’s self because they constitute the self. Since self-preservation, procreation, and empathy are vital to the preservation of humanity, or of genes if one believes in gene selection, it is to infer that, in most humans, the trio of instincts are very strong compared to other instincts. Therefore, most people will tend to not kill many humans nor abuse their power in ways which harm their self, because their instincts will stop them to preserve humanity.