It's horrible these events took place in schools, but in these cases anyway, I don't think it's possible to prevent this kind of tragedy by increasing security or anything like that.
So no, these events haven't changed my perspective on school security. Our school's biggest security problem is that it's a bit of a pass through for trespassers, and the school does have security guards to discourage them. I'm not really afraid for my children.
There are many other schools in the area that are no where near as safe as they should be, but the problem isn't security, it's the fact that the schools have very limited options what to do with thug students. Students are afraid of the bathrooms, they're afraid to ride the school bus. Teachers are afraid of some of their students. Some students are openly hostile, calling their teachers names, hitting them with f-word while refusing to do what they're ask to do, intimidating them, while the meeker, mellower students literally take a "lay low" tactic to avoid the bullies. The students are often terrified to "rat" their abusers, even when they're hit, because the punishment is too often a short suspension, and the students are terrified of the revenge when the perpetrator comes back to school or if the perpetrator comes looking for them outside of school. I know students and their parents who won't even attend their school's football or basketball games, because misunderstandings turn into dangerous fights, cars are vandalized, it's just a mess.
While school officials try to beef up security and minimize these kinds of troubles, the real problem in my mind is that they're just unhealthy institutions to begin with. When students are forced together who really don't want to be or deserve to be there, it naturally creates all kinds of social dysfunction.