Totally get it — my clarification was merely to note that there are different rules for police and civilians when it comes to being “free from fault”, which in fact leads me to be more comfortable when surrounded by law abiding citizens carrying firearms than if I were surrounded by law enforcement officers carrying firearms, if only because the civilians are held more accountable than police are for the moments leading up to a shoot/no-shoot decision, and act accordingly.
For example, a civilian carrying concealed can observe an altercation between two thugs throwing punches, and wisely decide to turn around the other way, and avoid confrontation, whereas an officer called to keep the peace is obligated to try and intervene in the situation — which can easily escalate in ways that the civilian actively avoids. And if the civilian *did* decide to intervene, not because there was any indication that someone was in imminent danger of death or great harm, but simply because they wanted to be a good samaritan and break up a fight, their self-defense claim in case of a shooting if the confrontation escalated would be subject to much more scrutiny.
Or, for a more extreme example, take a no-knock raid mistake. Police can shoot an innocent person, 22 times, by mistake, in a way that no civilian would get away with. You’re right, that at the point of pulling the trigger, as the SWAT team is raiding a house, with the occupant armed with a rifle (which was on safe, and never fired), could be seen as an act of self-defense — but only the cops are allowed to raid houses with military force.
Now, in the case where a response to a robbery report from a mentally ill woman escalates to knife threats from her for no reason whatsoever — I can definitely see how there can be a lot of lose-lose situations there. Hesitate, and you’ve gotten slashed across your carotid artery, and might not make it home. Or maybe she slices up one of her kids. Take action, and someone could die (even if you’re using “non-lethal” measures). People seem to think that magical stun guns exist like in TV and the movies, and don’t quite appreciate just how dangerous knives can be, much less how dangerous and unpredictable a mentally ill person can be with a weapon. The officers involved in that shooting came to help, with no aggressive intent, and were put into a no-win situation by a mentally ill person acting erratically and dangerously. It was a tragedy for all involved, to be sure.