I realise, as I write this, that there is a possibility we may be talking about two distinct things. As I read it in the text, by "intent to kill" Quirrell referred to Harry's reflexive interpretation of any fight as a fight to the death. If you are, instead, using the phrase to refer to the willingness and psychological ability to kill (whereas most regular people would find themselves instinctively aiming their knives away from vital points, and so on), then I have no disagreemen.

I'm actually speaking of neither of those things. Instead I speak of the things I allude to in my initial comment. Similar language is used to express related concepts fairly often in books on strategy as well as Eliezer's document on the virtues of rationality. I have also specifically asserted that I am not referring to the somewhat distinct concept on picking idiotic fights.