Identity Quotes in Ender's Game

What’s the difference between killing someone and being a killer? Ender admits to killing but keeps asserting that he’s “not a killer.” Basically, it seems like Ender is asserting that the difference between killing and being a killer is because he didn’t “want to kill them all.” Or is the distinction something else – is it a question of identity that Ender is refusing? (Like, what if you type – does that make you a typist? Well, maybe for the time that you’re typing it does, but what about after?) This is the major issue in the book, and it’s a question that we can’t answer.