It has been this way since he was 3...
I have been trying to gently guide his play to more rescue than kill type of games. SO far he shows no inclination towards less violent roles but I am working on it!
If he doesn't want to be the rescuer, would there be any violent play you'd find less offensive? In our house, the boys love playing 'Going on a zombie hunt'. It's like going on a bear hunt, only you're out searching for zombies and when you find them, they come after you, and you have to shoot them before they eat your brains. Violent? Yes. But, wow, are they proud when they save themselves! And I can't get too offended by the desire to kill a zombie.