The answer is simple: Mental illness. And you can't legislate against mental illness. You can't make it illegal. And you can't prevent it. It's simply a fact that there will always be that handful of wackos out there. Always were, always will be. The reason that these sorts of incidents seem to be on the rise, IMO, is simply that we hear so much about them. Fifty years ago, the incident in Nevada would be a local story, not a national story. These days, with all of our instant communication, it's a worldwide story. Unlike the way it used to be, these days we hear about every single such incident.