A relative minority of veterans of all the wars you cited actually suffered tangible, life-affecting trauma. We tend to read a lot about this type of trauma today because it gets so much publicity. But it's also a case of the news media playing up negatives to increase circulation. How much "news" value is there in a story whose headline is, "Vietnam Vet Leads Normal Life"?
As for Michael: World War II was considered a "just" war by the vast majority of Americans who fought in it; and nearly all physically fit men either volunteered or were drafted into the military. As we saw at the end of GFII, Michael was gung-ho to join the Marines. But in the Vietnam era, only a small percentage of draft-eligible men were drafted, which tended to make some of them resentful of those who had deferments or otherwise didn't serve. And more than a few American soldiers who fought in Vietnam questioned the justice or rationale for American involvement in that war. As a result, some (but not a majority) suffered from trauma.