The point of a "gun-free zone" is that there's a zero-tolerance policy for any weapon found there. People will point out that it doesn't stop mass shooters, and they are right, but that's also not their purpose (as depressing as it is, I can't think of something that will actually stop a crazed individual who is determined to kill a lot of people, unfortunately). I was in high school in the early 1990s (when, remember, gun violence in schools was at twice the level it is today, even with mass shootings) and I'd like to see the policy continued since I would argue it's a big part of why violence is so much lower in schools today than it was back then.

What that argument extension leaves out is that no one was packing assault rifles

People have been hunting with semi-automatic rifles for over a century. But, as a reminder, shootings in schools were more common in the 1960's, back when you could do that, then they are today.

What I want is for him to live in a community where no one has assault weapons in their closet.

Well, semi-automatic rifles are far and away the most popular class of rifle sold, so we need to figure out a way to live with them rather than wishing they would go away.