That article was 10% truth and about 90% rhetoric. Yes, you can't deny that this happened in this war and probably every war since the beginning of time. However, I don't think that you can accurately understand the context when you are half way around the world going to school or work everyday then going out on the weekends. The context is completely different for those who have been sitting in a desert hellhole for half a year or more without family or non-military friends whose job consists of trying to maintain some faux order without dying in the process.
So, I don't blame them for taking some pleasure out of killing someone. It's adapting to the situation they are in even if that means being desensitized to the moral rules that we claim to uphold here in the US. The concern comes more in the future when the enemy is not just who is shooting at you now but who is thought to be working to get you killed. That is when it all snowballs into another My Lai. Even if that doesn't happen, there are a multiude of Vietnam vets who came back from the war to become wife batterers, drug addicts, transients, and worse. Some soldiers can keep their combat lives seperate from their lives back at home, and some can't.