There's a lot of discourse going on here, but I'd just like to remind everyone that the perspective of 'there's a lot more mentally-ill cis white people, and they're allowed to own guns and commit mass murder' is giving a weapon to the ableist groups who'd like to strike all forms of neurodivergence from society, in entirety, in the stupidest possible way -- which is to say, eugenics.
Yes, it's highlighting hypocrisy, and that's good, but it's still granting legitimacy to the idea that a mental disorder or neurodivergence immediately renders someone dangerous to themselves or others. And the vast majority of mental and emotional concerns are undiagnosed through a combination of social stigma and shit psychological healthcare, anyway, so it's not like they're going to be going after anyone except the most visible. It's another layer of security theatre mixed with ableist hate and probably a good amount of warfare against other disadvantaged groups, as well.
(Hey, you know what exacerbates mental conditions as much as anything else? Poor living situations! Know who gets poorer living conditions? Visible minorities!)
In truth, the fact that the people who would shoot up a school are literally everywhere suggests to me another solution, e.g. banning guns overall. But that'd be ca-raaaaazy.