It's a difficult one this, I'm caught on both sides.
I served 17 years in the Army, and saw 4 tours of duty in Iraq, Bosnia, and a long stint in Northern Ireland. I've seen some horrible shit in that time which affects you for the rest of your life, seen good friends get killed, and serve an unhealthy hatred for races of people. I can see and understand why the Marine did it!
On the flip side, that Marine has received some of the best training you could ask for, the rules of engagement are very simple, and the Geneva convention rules are drummed into you from day one.
He made his mind up, did what he did for his own reasons, and that moment will haunt him for the rest of his days. It's a face he will never forget!
Don't be so quick to judge him guys.