I know a friend of his, a Delta sniper stud, who is helping folks with PTSD as well and is doing it as a part of his own recovery. He was deployed for 40 straight months. That's a lot of shooting for a Delta sniper.
Goes to show that it isn't as simple as "you need good guys with guns to stop the bad guys with guns." Awful ending to such an amazing life.
Simply because the vaccine doesn't work for an individual doesn't mean it doesn't work. You can reduce the incidence of shootings, even as you increase the risk of being shot. Theoretically, of course.