It's not the movies that make kids do stupid/unacceptable stuff. It's the personality of the kid. It's just like the phrase "if your friends jumped off a bridge would you too?" Some people will say yes because they observe other people doing it and assume it's socially acceptable. When I was a kid around 12-13 I did something like this too. I saw a movie (I forget the name of it) where a guy pushed another guy and he hit back. I assumed this was right so the next time someone touched me. I hit them with my full forced falcon punch. I got suspended for 3 days.
Ryan Gosling should not have taken knives to school, but it was not likely the violence in the movie that inspired him to do so, it was more likely the symbolism of toughness that inspired him. Parents can decide if movies are too violent for their child or not, and should exercise due dilegence.
Each child is different, and to some children watching a violent movie will not induce violence or lead to negative feelings. To these kids, the violence is simply a part of the storyline. Other children, though, may find violence scary and should therefore avoid violent films to prevent anxious thoughts and nightmares.
Yes, parents should allow kids to watch violent movies because it is not right to censor them. They should, however, discuss the problems of horror films. Gosling's parents should have warned him ahead of time and spoken to him about the fact that a movie is fantasy and should not be recreated.
The reason it feels instinctive to not let my son see more extreme screen violence is because I’m driven by the strongest parental instinct of all – to ensure my child feels safe. So when I protect him from violent imagery, it’s not because of an irrational fear that it’ll turn him into a bloodthirsty nutcase; it’s simply because I don’t want to scare him, which is clearly going to happen if I let him see certain films too early, much as I was scared by some of what I saw as a child.