This is a really tough one with legit arguments on both sides. This whole case hits super close to home because I grew up not far from where this happened.
I have a carry permit for defense, BUT... this kid took a gun openly to play soldier. You are allowed to openly carry firearms in WI, but you have to be of legal age and follow the laws (which he did not).
My 2 cents on this is no-one would have died if he hadn't taken the gun down there. Yes, the rioters were a mob of jackasses (to put it lightly) with a few of them chasing and attacking him. Yes, he was protecting himself, but he created that dangerous situation himself. I don't think he is an outright murderer who went there to shoot people, but I think he is an immature moron who wanted to play army soldier. He may not have premeditated the killings, but I do believe his actions in bringing the gun into the scene created the additional risk and he created his own situation of involuntary manslaughter. He poured gas on a fire and created the escalated situation himself. You have rights to do things, but you also have to live with the consequences of your actions.
Like I said - just my basic opinion. I grew up near there and grew up hunting, shooting, and being taught how to respect firearms and not treat them like toys. You have the right to carry, but you also have to have the intelligence to know if it's a good idea or not to do something. This kid is immature and was trying to act out his soldier fantasies until $@!% got real. The others who chased and attacked him were no better than him - they paid a price and now he has one due too for his equally moronic actions.
/my 2 cents.