I cannot believe that violence depicted onscreen actually causes people to act out violently. That's oversimplifying the issue. If somebody commits a violent act after seeing violence in a movie, I think the question that needs to be asked is: would that person still have committed the act if he had not seen a violent film?
Actors, I think, are all the same. Both Korean actors and American actors are all very sensitive people, and they are all curious to know what the director thinks of them and how they are evaluated, and they try to satisfy the director. And they like it if you listen carefully to their opinions and accept them.