I've been playing violent video games off and on for 30 years, but things have changed in the last few years. I think the level of realism now makes games fundamentally different with regard to how they affect players, especially young players.
Decades ago the military changed from using regular targets to using man-shaped silhouettes because they found that soldiers would freeze in battle when they had to shoot an actual person. The man-shaped silhouettes fixed this to a significant degree.
It seems reasonable to infer that spending hours a day training to eviscerate real-looking and screaming characters in a video game would also make it easier in real life.
The unbelievable gore now is a lot different than the spray of red pixels from games when I was a kid. I'm not sure warnings will help, but we should probably start looking more seriously at the issue.
What I would really like to see, are industry standards on some system which allows the gamer to control the level of gore in games from the menu, from none to whatever the designers dream up. Add meaningful parental lockouts to that, and then we could all decide for ourselves.