You're right, and I should have been more clear with the nuance I was trying to get across. Growing up, guns being used to indiscriminately kill other people was something that happened somewhere else, often associated with drugs/gangs. Even in my smaller city, there were simply some places you didn't go. But, no one considered kids showing up to a school and shooting people. Then Columbine happened which brought it out of the the big/inner city and into everyone's backyard. And around a decade later, Sandy Hook.

And to the original post, there's also an income inequality component. More well off parents probably felt (rightly or wrongly) they could move to a safer place. That feeling has been eroded through school shootings, no matter how statistically insignificant they are.