That's not exactly the point vec's making, max. Plenty of folks (i.e. the
wild majority) who are mentally ill don't shoot up schools, or even anything
else. Something like a quarter of the US has an active mental illness diagnosis during any given year, and far all there's too goddamn many of them the number of school shootings is only about one a week (i.e. 50-55 out of something like 82 million, which is a percentage so low the calculator on this computer gives up and resorts to scientific notation).
Nevermind that the vast majority of gun violence happens outside of schools, quite a lot of it inflicted by people that would pass through a psyche screening like greased owl shit, disproportionately on people who wouldn't or haven't. Vec's 100% correct when they say someone mentally ill is more likely a victim than a perpetrator of gun violence.
Like, frankly, it's one of the complications with the intersection of mental health and gun violence -- while many folks committing the latter are mentally ill to some degree, the vast, vast majority of folks who are mentally ill are not even violent, much less murderously violent and willing to resort to shooting people. Much of what mental health services do aren't going to have anything to do with folks that are a shooting risk, because even if absolutely no one slipped through the (underfunded, hamstrung by conservative shitheels) cracks there's just not that
many of them, and the way mental healthcare works just... isn't super good at identifying the ones that are.
It's one of several reasons why improved mental health services just wouldn't be a silver bullet, even if somehow conservatives stopped trying to sabotage it across the board and instead threw full throated support behind it in an effort to mitigate gun violence. It's just not very effective at identifying and preventing the problem in question. Good for a massive fuckton of
other reasons, but... not that one.
... all that said, if you're looking for the most effective mental health service to provide to mitigate mass shootings in particular, well...
studies have found (link to a vice report on one of them) that the single most pervasive commonality between shooters is that they're extremely likely (something like 70% or up, iirc) to be suicidal. So... suicide prevention would be the way to go, more than basically any and every thing else.
Coincidence that's one of the named and explicit targets of anti-school efforts by the GOP? One would hope it's just a coincidence, I guess...