Why did the Navy Shooter do it? Simplest answer is because he wanted to. He hated his life, he hated the people in it. He hated everything and everyone enough that the consequences weren't a factor. When these rampages happen everyone wants to think that the person just snapped. As though there was all this pressure and suddenly something inside just gives way and shazzam! a psycho killer appears where a regular nice guy used to be. I guess that it might happen that way, but my belief is that this guy fantasized about it. Thought about it. Told himself everyday as rude people ticked him off, as supervisors and co-workers stabbed him in the back etc. that "one of these days...to the moon Alice!"
In this case we'll never know. The difference between these days and the days of the Honeymooners is that violence is inculcated and nurtured within us by our non-stop culture of violence on TV, in moves, music and art, comic books, video games, and toys. In a world where a video game like Grand Theft Auto is a number-one best selling video game franchise, honestly were you expecting something else? It's not the guns it's the sick culture.