Post-traumatic stress is its own category of mental illness which doesn't have a genetic cause. Human beings were designed as sensitive and vulnerable organisms--we are easily damaged, and that includes psychological damage.
Human beings are not the superheroes (capable of sustaining all kinds of punishment or able to do superhuman things) that are portrayed in the video games that brainwash young people. We experience real pain when we are hurt, and when we are damaged, it takes a very long time to recover, if we ever do.
Because governmental leaders are committing the US to apparently endless wars, soldiers who have made a brave sacrifice in fighting for this country have, at a higher rate than in the past, become victims of PTSD.
In the Iraq war, it became government policy to prescribe a variety of psychiatric drugs as well as painkillers to troops. It is quite an instance of hypocrisy--our government is supposedly waging war on drugs while at the same time is doping up American soldiers to keep them performing.
Troops (another word for human beings wearing a uniform) have been traumatized partly because of the inhuman acts of violence they have been made to do by our government. Suicide is a leading cause of death among persons who have fought in Iraq.
Unlike in other major conflicts, there has been no draft to increase troop numbers in the "war on terror." Thus, people have been made to do three, four and five tours of duty in a row. This has pushed a lot of people past the breaking point. There are an estimated thirty percent of Iraq veterans who now suffer from war-induced mental illness.
A foot soldier isn't responsible for the atrocities of war. Often, they are put in that position by politicians. Some soldiers are still participating to avoid negative consequences such as a less then honorable discharge--which is something that could haunt them for life.
Many people who suffer from PTSD have never fought in a war. There is my own post traumatic stress which comes from rough treatment from other kids in the public school system, from abusive treatment I have received in the mental health treatment system, and from being otherwise victimized. And this includes being threatened at gunpoint, being otherwise threatened, and being forced into some altercations.
On top of post-traumatic stress that I experience due to events far in my past, I experience a constant, low-level state of crisis due to difficult events that have occurred in the past ten years of my life. Some of my PTSD is nobody's fault--caused by random unfortunate events.
This disorder, for many people, prevents enjoyment of "the now" and causes a person to dreadfully anticipate the next series of problems, or to fear that the traumatic event will happen again.
People can get PTSD from being abused or otherwise traumatized as children. People can get it through marrying an abusive spouse. People forced to grow up in a rough neighborhood are likely to have PTSD, and some have learned to mimic the violent behavior of others as a means of adapting.
Human beings are vulnerable creatures and we weren't designed to be treated roughly. Yes, our species has a long history of violence, war and of oppressing and being oppressed. However, just because violence and oppression have happened a lot in history, that does not make any of it good for us.
The self-perpetuating cycle of violence and abuse is a sickness, and must be resolved if we are to survive as a species.