PTSD is reassuring for me in a way - if humans were truly naturally murderous beasts, as some would like to insist, PTSD would be very rare or non-existant.
Read On Killing. Only psychopaths can kill without emotional consequences. People are naturally opposed to killing when it comes to dealing with members of the same species. Men can hunt and kill a deer. That's instinct. When confronting other humans, the instinct is to posture or submit. Same applies to most other mammals.
"It ain't over until it's over." -- Casey Stengel