There is one thing I should mention:
Akane did not merely talk the victim out of her criminal intent. She took concrete steps to demonstrate that she has the welfare of the victim in mind.
Consider this: the rapist showed the victim her psycho pass index: It was in the latent criminal stage. He then asserted that if the police were to lay their hands on her, she would be done. The victim's reaction suggests apparent belief. Thus, when the police first approached her, she may very well see them as enemies and refuse to believe anything they say.
When she was holding the lighter, however, Akane had shot another policeman who was about to shoot the victim. At this point, Akane had demonstrated with action that she might not want to harm the victim. At this point, the victim has more concrete proof that Akane could be her "friend," so to speak.
Thus, the fact that Akane managed to talk the victim down does not necessarily prove that Masaoka was wrong to want to use the tranquilizer, nor that the dominator's assessment was incorrect. Think of it as a natural example of the
good cop/bad cop routine.