I think that Lian is addicted to death, honestly. The rush that people can get when they have "power" over life and death. I think that is something that doctors feel in some measure, at least when they are able to save people. Probably what keeps them slogging in a very high stress job day after day.
I agree with Nephy on her definition on revenge vs. retribution. I think that revenge is often used by a party that believes they are wronged...case in point, when Adam kidnaps Kane and has Nye torture and top him. That can only be viewed as revenge imo, against Kane for trying to take Nye away, and against Nye for having loved Kane, in any way, shape or form. Knowing that would drive a personality like Adam's crazy and most likely allow him to think this is the best way to "pay" them back.
Retribution on the other hand, that is justice for wrongs that are so heinous that action cannot be denied, they must be stopped. Again, in any way, shape or form. I think that most acts of retribution fit the crime, but don't stoop to the same level, if that makes any sense. I could not see Kane kidnapping or using Adam for payback for what was done to him, I do see him kicking the shit out of him and putting him out of the "business" however. That is the difference in my mind.