So, what new laws do you propose?
Make murder illegal?
Make it illegal to shoot at people?
Make it illegal for a lunatic to have a gun?
Make it illegal to have a gun on school property?
Oh, wait......
There is evil in this world. No way around it. We can be prepared to face it, but we cannot avoid it.
Ding a ling a ding dong!!! Exactly right.
Oh but we can add Make murder with a gun even worse than murder any other way!
Crazies always were, still are, and always will be. You either defend yourself or not. How does not help anything?