Duplicity is a term used in the field of psychology to describe a person’s tendency to feel guilty for doing the “wrong” things. It is often attributed to being a psychopath, but I would suggest that it is really more of a result of being a human being.
In this case, duplicity is an issue with the protagonist of the game, Colt Vahn. I can’t really say I blame him for feeling that way. He’s not a perfectly nice person, and there’s something about him that makes me want to shoot him. But I’m not going to tell anyone to stop shooting him because, while he’s a great guy, there’s no reason to feel guilty for it.