Jim, it's not their training. It's what they had to deal with. It's a totally different war then fought in WWII. I've heard too many stories that just made me cringe. Could see how some could turn. BUT, at same time, those that turn that I know would never go on a shooting rampage, just a drinking rampage (and have seen it unfortunately). Those that have served in OIF/OEF in those roles could expand much more.
For sure it is a "different war"...not necessarily "better" or "worse"...but different. War is a nasty business regardless of the era. In addition to WWII, consider our Civil War, WWI, Korea, and Viet Nam. They were all horrific and bloody conflicts. Today's warriors are the best trained, and best equipped fighting force in history, but the effects of the horrors of war on the human psyche just haven't changed much over the years. When the WWII guys went over the edge, it was called "battle fatigue"...we all remember the scene from Patton when the young soldier was called a coward. Today we supposedly have a better understanding of what we now call PTSD, and try to accommodate the need of our returning warriors than they did in earlier times.
If you want to read an account of a Marine's life in the Pacific during WWII, I highly recommend With The Old Breed at Pelieu & Okinawa by E.B. Sledge. When I was in high school and college, I worked for a WWII Marine who made these same landings and recounted the events described in the book on a regular basis. For a similar accounting of the Viet Nam conflict, I recommend We Were Soldiers Once and Young by Gen Hal Moore. There are numerous other documentaries that are equally as good, but these two are special to me.
Understand that these comments are in no way meant to take away from the honor, committment and sacrafice that todays troops are making...just to say that that war and armed conflict is, and always has been, an ugly way to "solve" societal problems. Wars, if fought, should be fought by soldiers at least 50 years of age. By that time we hopefully would be smart enough to figure a way to solve our problems without killing each other....