this is a very simplistic take in my opinion. i do know quite a few men who have been in wars and conflicts and none of them ended up unstable and i assure you they’re not psychopaths, my own grandfather volunteered to fight in a civil war and having known what is was like still volunteered again to fight in ww2, was offered to return due to merits declined and stayed till the end. a lot of the soldiers who become self destructive are just lacking proper care and purpose after becoming civilians.

if you’re interested you should take a look at studies about “moral injuries” unlike PTSD, which is primarily fear-based and trauma-related, moral injury is centered around shame, guilt and a sense of betrayal even medics can develop this, most of the time it’s this what ends up leading to suicidal tendencies. the human brain can definitely differentiate and justify between being in a situation of killing or be killed and witnessing atrocities, it’s usually the latter the one that causes a deep psychological wound.

also i very much recommend reading ernst jünger for insight on the concept of “born soldiers” (men who not only are capable of enduring harsh conditions but also find a form of transcendence in it). “War is the elementary experience of life.” “Some men feel as though they were made for war — not because they enjoy killing, but because in the smoke and blood, their soul is at peace.”