I think you're on the right track. On Shell Shock- the doctors initially believed that these symptoms were being caused by brain damage, from the concussive force of being shelled; 8 men sitting a bunker, being shelled for 3 days non-stop, they believed this was causing concussions.

PTSD tends to manifest in people who experience horrific events where they had little to no control over the event. A bear mauling you, for example- that helplessness you feel? That is the root of PTSD. Rape victims? Probably similar to a mauling, depending on how brutal the rapist is. Car accidents? You were doing everything right, but some jackass swerved and hit you, fucking you up and killing your passenger friend. War? You're walking around, shells landing non-stop, occasionally you see one of your friends drop down in agony as he is ripped to bits by shrapnel. Or a sniper pops your friend's head clean off, and you have no idea where the shot came from and can do nothing to remedy the situation. The one common thread between all of these things: HELPLESSNESS. That last batch of shells missed you- but maybe the next salvo has a round with your name on it. And you'll never know what hit you- see, if you're being shelled, and you can hear the shells incoming, you're probably safe if you get down flat on your belly. However, if a shell is heading directly at you, you will not hear it. One moment you're fine, the next you're barely conscious, torn to pieces, have no idea what the fuck happened, you know you're dying, and there is nothing you can do about it.

PTSD is caused by helplessness in intense situations, usually involving violence.

Id be down with having major highways lined with the corpses of crucified criminals and corrupt politicians, as would I go to a live deathmatch for entertainment.