The human body has, basically, only 2 responses to a situation of panic or terror. Fight or flight. Sometimes both of these cross and cause the brain to be confused also. Sometimes the brain will shut down to protect the body, passing out. Screaming is a response, mostly primal, to warn others and to scare off the invader. Our modern society, and all the "brainiacs", try to curb these primal instincts. Some even say there is no such thing as an instinct and all is a learned response. I disagree with that, but who am I. You can't stop evolution. You can try to change somethings, like yoga to calm yourself, but in the end evolution and instinct win. Try to stop something when a sexy, naked woman rubs against you. I bet you can't.
Anyway, when something happens, especially to a young adult, who knows what their response will be. If they have never been in a certain situation before, such as a fire fight, then even they have no idea what they will do. Or, worse, what they are capable of doing. It is a clinical fact that both teenage girls and teenage boys go through a "brain rewire". Boys will actually not "snap out of it" until they are around 20-21 yrs old. Girls a little earlier. That is why between 15-20 most boys go crazy. Anyone here have any teenage kids? Exactly. Another example is small children. They have no remorse. That comes later. Children cannot look at a homeless man and think, "I feel sorry for him". Why do you think they hit other kids and don't really react when the other child starts crying.
Now back to what I was saying. Ever had a vasovagal response? I bet you have. Like when you see blood or watch someone getting an operation. Yep, cold sweat, fainting, ect. Even standing in formation for a long time will cause this. I've seen grown, strong, tough ass men, just fall out from seeing blood or a needle coming at them. Not to mention combat injuries. When I was shot I was actually conscious and kept going to a safe area. When another Marine came to help me, he was down for the count. They actually thought he was the one injured. You never know how you will respond until you have gone through a certain situation.
So, when we look at all those 18-19yr olds storming the beaches of Normandy (which, by the way, still boggles my mind) or the young country boy slapped into the jungles of Vietnam or the tough kid from the Bronx staring at a target through a scope, we have to consider all the facts of how they will respond. Put several of these brains together and there is a possibility of a serious problem. Schizophrenia manifests around the age or 17-25, same age as all those warriors.
Again, I am not defending the My Lai massacre, but the human body is capable of doing some seriously crazy shit. Nasty, dangerous, twisted, sick shit. And we need to understand that we are human. We can snap at certain situations and have negative responses to these situations. No matter what we do or try, what we were taught or learned, you really don't know what might happen when we see "red". And while seeing "red", if it exacerbated by others seeing red and their responses, it can become a real mess. We will at some point, all see red. It just matters how much red we see.