Lets for a minute if we can, take guns out of the equation. There are dozens of other ways for someone to accomplish their evil goals without guns. Instead look at the kinds of people that carry out these attacks.
What I see most of them having in common is they don't know how to handle disappointment, criticism, rejection, peer pressure, and failure. Misguided society and well meaning parents have created spoiled, inept, helpless, mentally unbalanced, over medicated social misfits. As long as everything goes their way, they get their new iPhones every year, aren't required to work, or even help out at home, they're fine! Tell them 'NO', tell them they can't have something, they need to make something of themselves, get a job, grow up, and god forbid act responsible and be held accountable all Hell breaks lose!