True--unless the actor (1) uses force when there is a reasonable alternative (preclusion), (2) uses excessive force, or (3) harms others by reckless disregard of risks.
Of course, there is the other issue--that of knowing that the person is in fact innocent.
Generally, one may use force when it is immediately necessary, to protect someone else from imminent danger--provided that that person would be lawfully entitled to use force himself. In some jurisdictions a reasonable belief may suffice, but in others, it will not.
We have often spoken here of the legal liabilities, both criminal and civil, attendant to intervention by the citizen who uses or threatens force. It is extremely important to realize that that risk is not the result of a legal system that just refuses to realize that the person who intervenes is the modern day equivalent of a benighted cavalier or the masked man with his faithful companion; rather, the risk lies in the very real possibility that the actor will turn out to be mistaken, or will otherwise muck it up. The legal system comes into play after there is evidence that the actor has improperly threatened or harmed someone else, whatever his perception of the situation or of his moral duties may have been.
I repeat in very clear words: It's not about being a hero, like you and others here seem to be repeatedly implying.
Some risks are worth taking. What those are, is for each individual to decide for himself.
The possibility of being confused about whether the guy standing on a table in the food court spraying bullets into a crowd of teenagers is certainly a real possibility
Now while that smart remark I just made applies to your statement, I'm also well aware that it may not be immediately obvious in a shooting situation who is doing the shooting. Sure, I could be completely off base and shoot another CWL holder who also decided to respond instead of the actual threat - A situation like that is even less likely than you and I ending up in an active shooter situation together at the same time, or even both of us being involved in separate situations at separate times.
In any case, I'm well aware how the legal system works - One must first make some sort of mistake in order to end up on the defendant bench.
There are a great MANY different issues to consider that will be different in each situation - If you go back and slowly read my comments, you'll see that I stated more than once that the reaction should be dictated by the situation, not by a one size fits all response. Your entire response seems to be nothing more than the 5th or 6th time someone has brought up potential legal ramifications.
I'm sure that since I'm a regular average joe and not employed in a first responder profession, that if I choose to respond, that will be a mistake. Everything I attempt will be a mistake, I'll shoot the wrong people, I'll use too much force, I'll find myself actually defending the bad guy instead of shooting him, I might even shoot myself. I'll surely end up dead and in jail though.
Seriously though, to get back to your list at the beginning of your reply - #1, a reasonable alternative - that only LEGALLY applies in states that require citizens to retreat before using force - I don't live in such a state. #2, in an active shooter situation, with someone shooting at me or others, deadly force is justified according to statute in my jurisdiction - so excessive force is irrelevant UNLESS I were to continue shooting after the subject was no longer a threat - I've been in only a couple use of force situations, but I'm pretty secure in my ability to judge when a person is a threat or not, especially if I'm the one dealing with that threat. #3 is the only caveat that fully applies, and only if my actions are judged reckless - Being former military with significantly more extensive firearms and tactical training than just the average guy on the street will aid me in avoiding the "reckless" judgement, and not simply by virtue of name dropping or whatever, but because I adhere to my training. While it's possible that a CWL holder accidentally shoot a bystander in such a situation, the bottom line is that in a situation like that, the Florida Stand Your Ground law protects me from litigation UNLESS I was truly reckless in my response to the threat.
Your comment seems to imply that no matter what a person does, if they choose to act in defense of others in an active shooter situation, they are making a mistake. I respectfully submit that you are wrong. Your arguments against acting all depend on the relevant use of force laws in your particular jurisdiction, and if legalities are important enough to a person that they would stand by and watch someone shoot an obvious innocent because it wouldn't be legal to respond, then that is not the kind of person I want anything to do with.
So in respect to your picking apart that generality I made, allow me to rephrase: It is NEVER wrong to defend an obviously innocent person's life if they are in immediate/imminent danger of death or great harm.
"The Law" has no bearing on that statement, and if there are consequences to doing the right thing, then so be it. Some things are worth dying for, and some things are worth stepping outside what society dictates we should do. After all - doesn't society say those of us who carry guns are wrong?
Further, I seem to notice everyone assuming "Shoot, shoot shoot" - I don't know about the rest of you, but I carry at least one knife, and a non-lethal option or two as well as my pistol. Even in an active shooter situation, shooting might not be the right answer.