Board Thread:Questions and Answers/@comment-29314611-20160915184039/@comment-28517148-20160916211120

That's true. But Rainbow is asking: what Frisk would do if he could make own decisions? Answer: that's unpredictable. It is required to have free will to make any decision and personality to determine it's type (genocide or pacifist). Both will and personality are part of soul that Frisk doesn't have. Even if he somehow manage to have one, it is still not enough data to describe his personality and  predict his choices.