Book Spoilers below!!:
I'll grant you that point about the word 'instinct' and how it is interpreted. I will say that he would keep on doing what he started in Asunder until he was stopped. I'll also take to task the general thought that he kills only people who want to be killed. As far as I know this info comes into play via Coles interatction with the people in question, it also seems that there is no indication that any of them actually tried to kill themselves before interacting with cole and his presence making it very easy for them to say they want to die. That aspect I always attributed to them.
This is pretty much how I see it too. He catches them at their most vulnerable, their most frightened--and then tells them how he can end their pain. How he can make it all go away. The fact that he offers them mercy, but kills them for his own needs and desires makes me think that while he may feel sorry for their situation, it had little motivation in casting their fate. Also, he knew what he was doing and he knew it was wrong. His reaction proved that when Ryhs called him out on it. He was ashamed and defensive--not because he didn't understand his crimes, but because he got caught at it.
I didn't like him the book. In fact, speaking of Evan Peters, Cole reminded me a lot of Tate from AHS. You sometimes thought he was torn between good and evil, that he struggled with it--that it ate away at his soul, but then..you'd see that knowing look, that hidden smile of satisfaction.
However I feel about Cole, I'll still give him a chance in the game. Who knows, maybe he will grow on me. I can't forget what he did, though. No matter what, he still......wait a minute, who was I talking about again?