Typically, church shootings have historically involved mass murder events: the intruder intends to kill as many people as he can, as fast as he can. He is
aiming for innocent people as he shoots.
Where in the world do people get the idea that the risk to these innocents from the murderer's
deliberately aimed shots is somehow lower than the risk to them from a defender's missed shots?

That's truly a nutty idea!
A defender -- even a "poorly trained" one who "doesn't have experience making decisions under stress" -- will not be deliberately mowing down innocents. Even if
one shot goes wild and hits a bystander, that bystander was destined to die anyway along with all other bystanders in range, from the murderer's bullets, if the defender wasn't there to stop the murderer. That's the cold hard reality.
Typically, mass murder events involve a single individual mowing down as many as 8 people a minute during the active phase; in 75% of cases, the killer brings more than one firearm to the scene along with extra ammunition in order to extend the killing phase as long as possible. The incidents are over quickly: almost always under 20 minutes, usually under 10 minutes, often under 5 minutes. The rapid firing rate and quick conclusion are almost certainly driven by police response times, because the active murderer typically continues to kill at his leisure until he is stopped by an outside force. Roughly half the time, the killer is stopped by an
unarmed civilian or group of civilians, a quarter of the time it's an
armed civilian, and a quarter of the time it's the arrival of the police that finally stops the killing. When police or armed citizens show up, the active killer takes his own life in 90% of incidents.
By definition, an active killer does not take hostages and he does not negotiate. He simply kills and continues to do so until he is stopped.
At 8 deaths a minute, waiting for the arrival of the police can be a very costly proposition. At 8 deaths a minute, almost anything the intended victims can do in response
should be done -- even if those things are nominally risky to others. There is no time to spare looking for a "perfect" response. The killings will continue until the killer is stopped.
At 8 deaths a minute, even if the defender missed the attacker with
every single shot in his entire magazine, and even if the defender hit a bystander with
every single missed shot! (need I say that's an unlikely outcome?) -- there would still be more danger to the intended victims from the murderer than there was from the incompetent defender. Especially since the vast majority of active killers immediately commit suicide at the first sign of armed resistance, which stops the killing just as certainly as if the killer is shot by someone else.
Facts drawn from Ron Borsch's work, found online at
Force Science News #97: Ohio Trainer Makes the Case for Single-Officer Entry Against Active Killers at Force Science News and
Force Science News #98: Solo Officers vs. Active Killers: Officers Speak Out at Force Science News and
ILEETA Report: Features of the Active Killer
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