I know people that, if their goal was destruction of a school, ALL the children and teachers would be dead. And it would be so much easier to do. And the likelihood of them getting caught would be minuscule.
Further, a gun would be impediment in achieving their goal.

Exactly, mostly what keeps us safe is that most of the time people do their jobs and super crazy homicidal maniacs are not walking free and there are not that many such people to begin with. then sometimes people call the police and FBI on someone over 45 times and nothing is done and then they blame guns being legal for law abiding people when he goes on a spree in a gun free zone where people cannot carry guns. He does claim to have been shot before yet he wouldn't answer my question about whether the person who shot him was allowed guns.