I would love to see some of your suggested approach. Any action towards helping the situation (which is NOT NORMAL) will be good. Any action at all.
Any step in the direction of reasonable, thoughtful gun control will also be good.
No one wants to take 'gun rights' away, but a tragedy consists of the person (mentally ill or otherwise), the access to mass-killing weapons (AR-15 or otherwise), opportunity (location/targets etc). You only need to take away one of the three to prevent the next tragedy.
The person (mental health or other otherwise) is hard to determine and impossible to predict/prevent at any moment (even with medication/counselling/mentoring/help). That person can snap at any moment in time. Or that person is just plain evil and not mentally ill (we have some of those here, whether we like it or not).
The opportunity (going to school) is unavoidable. They are KIDS!!! It is a SCHOOL!!! (I have kids of school age, and this FRIGHTENS ME every day)
So, the most logical way to handle is the access to weapons. There is no reason for military-grade weapons whatsoever. Want a handgun/rifle for personal safety? yes, ok. Hunting rifles, yes, ok. I may not personally own one but I respect those who wish to own one. But why is a military-grade weapon needed unless you actively serve?
Easy access to guns is a huge problem...unfortunately we only have to look to Los Angles and Chicago to see the infiltration of guns into the inner city by the government. This is an issue that has been around since the 80's. Any digging on the matter and you will find accounts of train cars filled with guns stopped in Compton, the doors open for all to take. Or Chicago where boxes of guns are left in alleys to be found by passer-bys.
But these are conspiracy theories, so let's deal in facts. It is "easy" to build, from scratch, your own gun. Back in the day these were called zipguns. Now, with modern manufacturing, and I'm not even talking about 3d printing....just modern tools you can purchase cheaply at a Harbor Freight, you can build an AK-47 or an AR-15.
Note I used the word "easy". There is skill involved, machining and such, but nothing a motived learning can't pickup. Machine shop in high school would be enough for most.
I guess what I am getting at is that to solve the Killing Problem requires more than fixing the Gun Problem. Yes, we need to fix easy access, but more importantly, we need to fix the reason young men kill.