So the shooter is certainly rational, we don't have to assume.
From what rational point of view is it that one decides to go and kill any number of innocent people? You assume that every mass shooter has the intention of racking up some "score" but that isn't the case. Many of these shooters would have done what they did whether they killed 5 people or none.
Being able to cloth yourself or use a gun isn't rational thought either. There are plenty of irrational people dressing themselves(look at politicians), and plenty more who own guns.
Without their cooperation, it is impossible for him to get a clear shot on anyone.
Except if they are in an office, classroom, church, or any other enclosed space where someone can't "take control" of the situation.
No, educate them to realize that a gun does not imply death.
What else does a gun imply outside of a gun range, hunting ground, or in the hands of police officer?