The fact is: That rifle is called and classified as an "Assault rifle". Not a "Defense rifle". It was not created to defend. It was created to assault, or attack.I've answered that question several times now.... No attacking someone retreating from a scene is most certainly NOT self-defense. It's one of the first things they teach you in concealed carry class. If an assailant stops his attack and then retreats, they are no longer an imminent threat to you and you cannot shoot them. If you do, you incur significant legal risk.
Even the bogus claim of SYG doesn't apply here either. Those people were not standing their ground, they were advancing, attacking a kid who was trying to retreat from the mob. If anything, the people who attacked him and shot at him are the ones who should be in court right now.
Now, to your scenario of the three guys..... So a gang of three armed thugs is about to corner your wife in an alleyway as she's trying to get to her car. One of them tries to grab her gun and she shoots him in obvious self-defense. Are you suggesting that the remaining two are now legally allowed to shoot her in self defense because she shot first? KR didn't even shoot first in this event. The mere act of those three attacking first removes any sort of victim status from them. THEY are the assailants and lose all claim of self defense. I'm honestly not making this up.
There are defense weapons, but that is not one of them.