What the standards are and what actually happens in war are sometimes different. Barbaric behavior among combat soldiers isn't new and isn't exclusive to current operations. Filming it and posting it on the internet for all the world to see is what is new. We shouldn't be surprised that bloody war can sometimes bring out the worst in young men. We can't condone it but we can surely understand it.
American soldiers have always been expected to adhere to higher standards of conduct in all the ranks. Sure there are always going to be exceptions but that doesn't change the standard. Even if you agree we should be there or leave as long as we are there we should conduct ourselves by a higher standard than anyone else.