Explanations of the men's actions
This movie isn't anti-military, it's anti-war. It isn't clear what happened to the 3 guys over in Iraq/afghanistan but the viewers were lead to believe that they did something wrong, maybe or maybe not illegal, that lead them to being dishonorably discharged. These 3 guys probably suffered post traumatic stress disorder PTSD. The fact that it's only been 18 days since they've been back makes it more understandable their reactions to their best friends death. Jimmy Wallace is the man who saved their lives, but we don't know what exactly he did.
It's implied that they are hunting illegally because it's not hunting season. You take 3 guys who 3 weeks ago were killing people legally, give them alcohol and give them guns, throw in a very aggressively flirtatious woman and you have a disaster going to happen. Let me be clear, she did nothing to deserve attempted raped, heck, NO ONE DESERVES to be raped for any reason. What she did was self defense. But her actions lead to his actions. He committed a crime, she did not commit a crime.
Suppose I have a concealed weapons permit where I can legally walk around carrying a gun. I walk around a dangerous neighborhood carrying a $10,000 in cash and flashing it around. I'm doing nothing illegal. Some guys approach me with the intent to rob me, brandishing knives or some other weapon. I have the legal right to shoot them with my gun if I feel my life or property is in immediate danger. You can do nothing illegal but your actions increase your chances of being a victim of a crime. You leave a wallet or purse, electronics in the front seat in plain view locked in your car - that increases the chances of your car being broken into.
I am not condoning any type of criminal behavior. I'm just trying to explain how certain criminal behavior may occur.