It's a complex problem with a lot of moving parts but I'll try to tackle it.
Since the end of WWII, the United States has been involved in a number of unpopular wars with ambiguous outcomes and in support of dubious allies. Korea was just the first but it was followed by Vietnam, Panama, Gulf War !, Gulf War II and Afghanistan.
Unlike WWII, none of these wars has been a clear-cut victories and a "good war" like WWII that the people could all support.
Often times we found ourselves supporting an ally that wasn't a hell of a lot different than the enemy.
In many of these wars the indigenous military ran a lot more than they fought and shot a lot more civilians and suspected spies than enemy soldiers.
When soldiers from these conflicts came home, they were met with apathy, ridicule and even hostility.
While WWII veterans were lauded and praised, Korean and Vietnam war veterans were ignored for the most part.
Post-WWII war veterans experiences were difficult, ugly and were often shrouded in secrecy. Many were told never to discuss operations that until this very day remain classified. So the foundation is laid for the silence: Never talk about it.
Almost all of these veterans suffer from Post Traumatic Stress Disorder to some degree, which I described in Valhalla. PTSD manifests itself in a number of ways and alcoholism and drug addiction is quite common and difficult to treat when you have a patient with numerous traumatic memories who can't find relief in any other way.
The symptoms of combat related PTSD that I described in Valhalla are alcoholism, drug addiction, sleeping difficulties, nightmares, flashbacks, social and family difficulties make it difficult or impossible for a sufferer to function successfully in society. In many cases its a degenerative condition and the PTSD sufferer's life falls apart over time. It becomes a downward spiral and the symptoms grow worse.
In many ways Never Talk About It makes things much worse. It is very difficult to get vets to confront these traumatic memories in a therapeutic setting. Many just think they are crazy and suffer in silence until a lot of damage has been done or there are serious personal and legal consequences.
It's no surprise that many of these guys end up homeless. The treatment that they receive on the streets as homeless people is disgraceful. They can become victims or be exceptionally violent if cornered or if they are having a flashback.
It is a complex problem that our society has yet to successfully cope with and the Afghan and Iraq Wars have added an entirely new generation of vets with crippling psychological problems that are progressive and deadly. Already we are seeing spikes in suicide rates of active duty personnel. If history is any guide, this will only get worse in the decades to come unless more effective treatment methods are used and our society treats this issue as a medical problem rather than a legal one.