On May 23, 2014 Elliot Rodger went berserk and killed 6 people before committing suicide. For several reasons the incident received an unusual amount of publicity and various people with axes to grind have attempted to draw lessons from it. However I think the main lesson is just that crazy people sometimes do crazy things.
Most incidents like this are perpetrated by mentally ill people and this case doesn't appear to be an exception. Of course there is some danger of circular reasoning when there is little independent evidence of mental problems prior to a killing spree. However that was not the case here.
I would define mental illness as mental abnormalities which cause problems for the subject. By this standard it was clear to many of the people around him that Rodger was mentally ill. What was not so clear was that he was dangerous. It may also be that his mental illness was not of a common type like paranoid schizophrenia but this does not mean he wasn't mentally ill at all. He was obviously abnormal.
It is a mistake to ascribe too much meaning to the actions of a crazy person. Their erratic random actions will sometimes by pure chance appear carefully planned. This doesn't mean they were. In this case Rodger achieved great notoriety in death but I am unconvinced that was his plan.