The statement in the title of this post is a common belief in spiritual and religious circles, but it appears there’s some hard evidence that when you harm others, you harm yourself as well.
According to a press release from the Association for Psychological Science, researchers looked into why it is that some soldiers (31.6%) who have traumatic combat exposure develop PTSD.
It seems that three factors are important: age, a history of childhood physical abuse, and harming civilians or POWs.
…childhood experiences of physical abuse or a pre-Vietnam psychiatric disorder other than PTSD were strong contributors to PTSD onset. Age also seemed to play an important role: Men who were younger than 25 when they entered the war were seven times more likely to develop PTSD compared to older men. The researchers also found that soldiers who inflicted harm on civilians or prisoners of war were much more likely to develop PTSD.
The combined data from all three primary factors — combat exposure, prewar vulnerability, and involvement in harming civilians or prisoners — revealed that PTSD syndrome onset reached an estimated 97% for veterans high on all three.
So harming others does seem to play a role in causing mental harm to ourselves — at least for soldiers who have experienced traumatic combat.
The article is “The Roles of Combat Exposure, Personal Vulnerability, and Involvement in Harm to Civilians or Prisoners in Vietnam War–Related Posttraumatic Stress Disorder.”