Conflating two things. Obviously if you have more strict gun controls, you'll have lower "gun violence" or even "deaths by gun". But that's circular. The question is whether actual overall crime/violence/murder rates are lower because of gun control and there's very close to zero evidence that one affects the other. But we were talking about mass shooting events, and how to prevent them. Clearly we can't prevent them via gun control, so why not allow legal changes (like more concealed carry and removing gun free zones around schools) which would mitigate and lower the rate of such shootings?
These two are so mixed up right now. Gun-related homicides in general don't seem very related to the mass shootings that pop up on occasion, other than both using a gun of course. On one hand you have people who have a relatively clean slate, peppered with a touch of concern about their mental health going ape-sh*t on a school. The other extreme you have a career criminal spiraling down a violent path of crime/drugs/gangs/etc culminating with a shooting, maybe several times.
I'm not sure how you can really stop a person determined to go out in a 'blaze of glory' though. Any practical defense a school district can afford can be fairly easily overcome by a reasonably determined attacker. I'm not sure spending millions of dollars on armed guards, gun safety training, or whatever is really the best use of money for a school district struggling to educate their kids.
I dunno, our high school security officer dealt drugs to the kids for years before he was caught. I would have hated to have given him a gun on campus. On the other hand despite the school being a gun-free zone guns were commonly brought to school anyway. Especially during hunting season there were always guns in cars in the parking lot. I never heard of any trouble coming from that, however there was the kid who pulled a knife on one of the other students in front of me in the hallway. On one hand it was crime without a gun, on the other that was unsettling enough without imagining him with a firearm.
I guess in the end when I hear gun-free zone I think "cheapest and least controversial way to address a problem" more than a best solution. I'm not sure if there's really a more practical way to address things. Massive school shootings and other mass-murder events are thankfully rare, and I'm not sure one can really afford to spend so much money on such an isolated problem. Again though, I'm going on the assumption anyone bringing a firearm onto school grounds would have to be trained somehow and that they wouldn't allow just anyone to bring a weapon there. Liability reasons if nothing else. Crazy guy kills people and it's a tragedy, your guy kills people and it's a lawsuit.
There, now you can read a wall of text from me for once.