Something that just crossed my mind: I have anger issues and playing shooting games allows me to express my emotions. I do not wish to kill but sometimes the sound of a bullet ihitting someone's face and they fall to the ground like a ragdoll calms me. Why? Because it sets my adrenaline to a normal pace. Same when my other emotions act up.
I have anger issues as well, and i enjoy shoving a knife into some sangheili's face, or beating a zombie's face in with a cricket bat. It helps me get stress out