The two factor of PTSD "posits that PTSD develops from an initial phase of fear acquisition through classical conditioning and is further maintained through instrumental avoidance behaviors.... various cues become associated with 'intense fear, helplessness or horror' and acquire the capacity to evoke strong emotional responses on subsequent occasions when the traumatic events is no longer occurring. Quickly, individuals learn to avoid these cues, but the avoidance prevents natural extinction from occurring... Although functional in the short run, avoidance thwarts corrective learning experiences."

BT Litz, et al, "Moral Injury and Moral Repair in War Veterans" from Clinical Psychology Review.

PS. There is a great series about Moral Injury in Huff Po that you should check out.