"[...] but in the hands of a lunatic having to pause to change magazines may give the valuable few seconds for the situation to defuse."
Mass shootings have involved the shooter having to change magazines several times. Military style weapons are designed for a quick change in battle. Notice how many times in war zones you see two magazines taped together - so only an inversion action is needed rather than pulling one from the body.
Even where intervention is possible at close range - it needs people to make a potentially suicidal counter-attack - rather than a self-preservation retreat. Enough time to defuse a situation verbally is possible only when the shooter voluntarily pauses.
Biting the hand that feeds IT
