This thread wasn't really meant to be a morality topic, but...
1. Calling Vang a hero might be a bit too far.
2. Calling him a straight-up cold murderer might be too far too.
Vang was originally in the wrong. He shouldn't have even been there. Also, from his own account, he checked a person whom he already shot. The person was already disabled from combat, but he killed the person anyways.
That being said, it was a stressful situation. It would be hard for anyone to keep all these moral and legal issues in mind while guns are being shot. Moreover, if Vang was a straight-up cold murderer, he would have shot the white people from the tree stand. Clearly, Vang was trying to leave, but somehow he didn't.
No one really knows what happened in those woods but the people who were there. Who shot first? Whose life was in danger? The white people's account is not consistent or even realistic. Vang's actions were brutal. The white people are dead, and Vang is in prison.