I remember a documentary I once saw about monkeys. It was amazing and funny to see these animals display the full range of emotions that we do, especially fear. The researcher in it said, "All species of monkey commit murder."
What I'm saying is that the human specie has not become sophisticated enough (IMHO) compared to our distant relatives to responsibly and safely wield such efficient killing machines. Until humans move forward, our emotions (especially fear) will always get the better of us. Fear is a great firearm purchase motivator.
Look at many of these school shooters. They were bullied (so was I). It's a really powerless and fearful feeling, especially the fear that it will go on forever. But ah, here comes a fast-firing way to regain power and make them regret ever torturing you. I'll just say I'm glad there were no guns available to me; my mind was immature and impulsive.
The more something is available, the more likely it will be used. Look at weed in Colorado, or Coke Cola around the world, or coal, or cars, or phones, or guns...
With guns so prevalent and humans so fallible I don't see a way out.
Countries with strict gun laws in Europe rarely have anything like this.
To me, shootings prove that monkeys can't handle firearms, so let's make them more available!