The mere presence of weapons can increase aggression—called the “weapons effect.” Weapons are theorized to increase aggression by priming aggressive thoughts. This research tested the robustness of the weapons effect using two large representative samples of American adults (total N = 1,097). Participants saw photos of criminals, soldiers, police in military gear, or police in regular gear with guns. Experiment 2 also included a condition with photos of Olympians with guns used to shoot inanimate targets. The control group was police in plainclothes without guns. The accessibility of aggressive thoughts was measured using a word fragment task (e.g., KI_ _ can be completed as KILL or KISS). Photos of individuals with guns used to shoot human targets primed aggressive thoughts, regardless of whether a “good guy” (soldier, police) or “bad guy” (criminal) held the gun. Photos of Olympians with guns used to shoot inanimate targets did not prime aggressive thoughts.
I think the author was “primed” with their own conclusion. When I think of “kill” in the context of a “good guy” with a gun I don’t think of aggression. I think of it as a strong defense.
See also the fairly neutral, Here’s what can happen to your brain and body when you shoot a gun.