If I were trying to convince someone on the other side, I think I'd start with that it was self defense, and then move into whether it was right for him to be out there after.

For someone to go all the way from "crazed right wing shooter" to "hero" is a very big leap, but maybe they can accept that he shouldn't have been out there, but he was attacked and acted in self defense.

Self defense is the easy truth that serves as the thin edge of the red pill wedge. The question of whether it was right or wrong for him to be there defending businesses can be addressed later.