Fact
He was 17. It was illegal for him to posses that rifle. In his home state you have to be 21, in wisconsin you have to be 18. This was crime 1.
Crossing the state line with an illegally possessed weapon is a pretty big deal and a big fat number 2 on the crime list. (So in reality, trying to engage in apologism based upon an incorrect distance is disingenuous at best, weak and lazy at worst)
Wisconsin totally allows for the use of deadly force in self defense, but the caveat is that you cant be committing a crime while that use of force happens. Which we addressed above he was actively committing a crime by possessing that rifle.
Wisconsin has a Castle Doctrine. But you can only use deadly force if the perpetrators are in your dwelling or your place of business. For a place of business you have to own this, or be in charge of operations of the business. You can not just post up to protect a random business, also you can not chase people if they decide to retreat like This 17yo did. Wisconsin V. Charles L Chew is the case law. If you want to have a look.
Its not self defense when you get in your car with a rifle, drive 30+miles to another town, and walk the streets with a rifle.
He had every option to stay home but he chose to get involved in this situation with the plan to be involved in confrontation(hence the rifle) also in Wisconsin self defense law you cant be the instigator and then claim self defense. He became the instigator the second he pursued.
The only people defending themselves were the ones being shot at by am angry little racist cunt who turned up armed and started firing on people.
You right wingers will engage in apologism for absolutely anything, from terrorism to the rape of children. I'll take your lessons on morality with a pinch of salt.