I've seen a lot of posts regarding why the little maniac did what he did, but I think it can be summed up in one paragraph:
Elliot Roger grew up steeped in liberal dogma, subscribed whole-heartedly to progressive ideology, and possessed an entitlement mindset that you would expect from a Red Diaper Doper Baby that grew up in Hollywood. He was a microcosm of the Democrat Party; emotionally stunted, sexually frustrated intellectual midgets who think that the entire world owes them something. And his actions are also a microcosm of what the Democrat Party wants to do if they don't get their way.
The fact that the Left is once again desperate to pin this guy on any kind of right-wing group only shows that they know exactly who and what he is. They look at Elliot Roger, and they're staring into a mirror.