I know what you are saying... BUT... You're mixing CIRCUMSTANCES. The case you are referring to was NOT a case involving a citizen involving themselves with an active shooter. The topic/point of the thread is CIVILIANS using force to inject themselves into an ACTIVE SHOOTER situation and then using force.
You have just as much "authority" to "use force to protect" as any cop does... and your actions and the results face the same legal test as a cops would. Perhaps you misunderstood the context of my post.