“tt would be better to hire retired policemen and military types”
NO, no retired police types. The guard needs to be physically fit, agile, fast and a crack shot. A retired cop doesn’t fit that bill. Shooters tend to be young and fast. A guard as physically fit as the shooter is vitally important. Otherwise, add one dead guard to the rest of the dead.
Also, a guard has less “skin in the game”. When SHTF, he has less incentive to in fact engage the shooter and risk his life (very cushy and safe up to that point) where he is not involved at the moment; his prime motivation at that moment will be to “call for backup”, waiting for others to engage the attacker. Happens too often.
An armed teacher, on the other hand, is the target (or a close part of the targeted group) and is highly motivated to stop the shooter RIGHT NOW as the only path to safety.