Longenecker gets it!
1. Lethal force without having to wait, obtain permission, or find the time to break away and notify others (and wait some more!). Already on the books. Don't make malls an exception to this: Include them.
2. Authority is already in place within the citizen. It's time to stop obfuscating it for the privilege of shopping there. One can act with lethal force when facing grave danger. One can come to the aid of another. This is nationwide but for a small few silly and unfriendly jurisdictions. Check your state for silly, unfriendly laws that say you have to run or something. How many of these nine ran?
3. Concealed weapon keeps the aggressors uncertain as to who will respond immediately. The idea is not entirely to dissuade a killer from shooting a mall's patrons – the idea is to stop him immediately. Citizens have that authority. Why hide or discourage it?